Computer Beginner Guide

Spam is geek terminology for unsolicited junk email and messages. Spam is fast becoming a huge problem. It’s starting to cost corporations millions of dollars each year to filter out spam, and handling spam has required companies to increase their server storage space and Internet bandwidth for all the extra traffic it generates. Once you give out your email address to a company, it may be sold to other companies. Those other companies quite often sell your email address to other companies, and so on into infinity. The following are some of the most common ways people unwittingly offer their email addresses to companies: Filling out online registration forms Entering contests Engaging in online discussion groups Filling out online surveys Choosing a common name for your email address If you belong to America Online (AOL), having a member profile and/or participating in chat rooms Also, some companies use a method called a dictionary attack. They compile many c...

Email hoaxes are a modern version of urban legend, or folklore, stories. When I was growing up as a child, we were told to be careful of any apples we received while trick-or-treating during Halloween. Apparently, as the story goes, some people were putting razor blades in apples, making them hazardous to eat. The New York Times (10/28/70, page 56) and even the “Dear Abby” column mentioned this potential threat to concerned parents. Years later, researchers Joel Best and Gerald Horiuchi studied national crime data from 1958 to 1985. They did not find a single reported incident of a razor appearing in an apple, or any other fruit or candy for that matter. The children who were harmed by tainted candy, as reported during those years, were harmed by members of their own family. I mention this story because the Internet has created a new and fast way for the distribution of information. Some of this information is really nothing more than misinformation written by pranksters ...

You might be a little intimidated by all these acronyms, abbreviations, and specifications-speak. Don’t be. Heck, I had to look most of that stuff up as I was writing this, just to make sure I was up-to-date! In most cases, HTML and XHTML concepts are surprisingly simple after you have the basic sense of the way the markup works. It may be comforting to keep repeating to yourself that HTML isn’t anywhere near as complex as programming. Whereas programming is the process of creating scripts or applications using complicated computer languages such as C++ or Java, creating Web pages is generally referred to as authoring. That’s because most of what you’re doing is simply entering text, and then adding codes in and around that text to organize it on the page. From there, you add elements that cause images or multimedia to appear on the page, or elements that make the page look better. That’s what a good portion of this book deals with and it’s all you need to know to put toge...

As you’ve seen, HTML is a markup language designed to combine text, multimedia, and hyperlinks to create a Web page. HTML is also a moving target, though, because several different versions have been introduced since it first appeared in the early 1990s. Although each version has built upon the last, and most Web browsers are designed to be “backward-compatible” with previous versions, it’s important to know something about current and future versions of HTML. The World Wide Web Consortium is responsible for creating the specifications that other companies adhere to (for the most part) when creating such things as Web browser applications and devices for viewing Web pages. The W3C is an industry group, founded by Tim Berners-Lee, that includes most of the major players in the corporate world of Web development (such as Microsoft, Netscape, AOL, and AT&T). One of the tasks the W3C undertakes is maintaining the HTML specification. Because technology is always changing, ...

The World Wide Web isn’t a particular place on the Internet, nor is it a particular computer or something that you can “log into.” Instead, the best way to describe the Web is as a service on the Internet. Using certain protocols, computers that are designated as Web server computers—because they’re connected to the Internet and run Web server software—can respond to requests from client computers running Web browser software. Every computer on the Internet has an address. When a request comes into a Web server computer from a particular address, it responds by sending the requested file back to that address. When the browser application receives that file, it reacts accordingly, generally by displaying the file as a Web page, image, or multimedia element within the browser’s own window. In other cases, the browser might recognize that it can’t handle the file, so it hands it off to a helper application or saves the file in a designated place on the client computer’s hard ...

There are many services which a site may wish to provide for its users, some of which may be external. There are a variety of security reasons to attempt to isolate services onto dedicated host computers. The services which a site may provide will, in most cases, have different levels of access needs and models of trust. Name Servers (DNS and NIS (+)) - The Internet uses the Domain Name System (DNS) to perform address resolution for host and network names. The Network Information Service (NIS) and NIS+ are not used on the global Internet, but are subject to the same risks as a DNS server. Name-to-address resolution is critical to the secure operation of any network. An attacker who can successfully control or impersonate a DNS server can re-route traffic to subvert security protections. For example, routine traffic can be diverted to a compromised system to be monitored; or, users can be tricked into providing authentication secrets. An organization should create well kn...

There are many services which a site may wish to provide for its users, some of which may be external. There are a variety of security reasons to attempt to isolate services onto dedicated host computers. The services which a site may provide will, in most cases, have different levels of access needs and models of trust. Services which are essential to the security or smooth operation of a site would be better off being placed on a dedicated machine with very limited access, rather than on a machine that provides a service (or services) which has traditionally been less secure, or requires greater accessibility by users who may accidentally suborn security. It is also important to distinguish between hosts which operate within different models of trust (e.g., all the hosts inside of a firewall and any host on an exposed network). Some of the services which should be examined for potential separation are outlined in the section on service protection. It is important to reme...

This service performs two functions. The first is the detection of the occurrence of a threat. (However, the detection does not occur in real time unless some type of realtime monitoring capability is utilized.) Depending on the extensiveness of the logging, the detected event should be traceable throughout the system. For example, when an intruder breaks into the system, the log should indicate who was logged on to the system at the time, all sensitive files that had failed accesses, all programs that had attempted executions, etc. It should also indicate sensitive files and programs that were successfully accessed in this time period. It may be appropriate that some areas of the LAN (workstations, fileservers, etc.) have some type of logging service. The second function of this service is to provide system and network managers with statistics that indicate that systems and the network as a whole are functioning properly. This can be done by an audit mechanism that uses ...

The data and message integrity service helps to protect data and software on workstations, file servers, and other LAN components from unauthorized modification. The unauthorized modification can be intentional or accidental. This service can be provided by the use of cryptographic checksums, and very granular access control and privilege mechanisms. The more granular the access control or privilege mechanism, the less likely an unauthorized or accidental modification can occur. The data and message integrity service also helps to ensure that a message is not altered, deleted or added to in any manner during transmission. (The inadvertent modification of a message packet is handled through the media access control implemented within the LAN protocol.) Most of the security techniques available today cannot prevent the modification of a message, but they can detect the modification of a message (unless the message is deleted altogether). The use of checksums provide a modif...

The data and message confidentiality service can be used when the secrecy of information is necessary. As a front line protection, this service may incorporate mechanisms associated with the access control service, but can also rely on encryption to provide further secrecy protection. Encrypting information converts it to an unintelligible form called ciphertext, decrypting converts the information back to its original form. Sensitive information can be stored in the encrypted, ciphertext, form. In this way if the access control service is circumvented, the file may be accessed but the information is still protected by being in encrypted form. (The use of encryption may be critical on PCs that do not provide an access control service as a front line protection.) It is very difficult to control unauthorized access to LAN traffic as it is moved through the LAN. For most LAN users, this is a realized and accepted problem. The use of encryption reduces the risk of someone capt...

This service protects against the unauthorized use of LAN resources, and can be provided by the use of access control mechanisms and privilege mechanisms. Most file servers and multi-user workstations provide this service to some extent. However, PCs which mount drives from the file servers usually do not. Users must recognize that files used locally from a mounted drive are under the access control of the PC. For this reason it may be important to incorporate access control, confidentiality and integrity services on PCs to whatever extent possible. According to [NCSC87], access control can be achieved by using discretionary access control or mandatory access control. Discretionary access control is the most common type of access control used by LANs. The basis of this kind of security is that an individual user, or program operating on the user’s behalf is allowed to specify explicitly the types of access other users (or programs executing on their behalf) may have to in...

The first step toward securing the resources of a LAN is the ability to verify the identities of users [BNOV91]. The process of verifying a user’s identity is referred to as authentication. Authentication provides the basis for the effectiveness of other controls used on the LAN. For example the logging mechanism provides usage information based on the userid. The access control mechanism permits access to LAN resources based on the userid. Both these controls are only effective under the assumption that the requestor of a LAN service is the valid user assigned to that specific userid. Identification requires the user to be known by the LAN in some manner. This is usually based on an assigned userid. However the LAN cannot trust the validity that the user is in fact, who the user claims to be, without being authenticated. The authentication is done by having the user supply something that only the user has, such as a token, something that only the user knows, such as a pa...

A variety of threats face today's computer systems and the information they process. In order to control the risks of operating an information system, managers and users must know the vulnerabilities of the system and the threats, which may exploit them. Knowledge of the threat environment allows the system manager to implement the most cost-effective security measures. In some cases, managers may find it most cost-effective to simply tolerate the expected losses. The following threats and associated losses are based on their prevalence and significance in the current computing environment and their expected growth. The list is not exhaustive; some threats may combine elements from more than one area. Errors and Omissions Users, data entry clerks, system operators, and programmers frequently make unintentional errors, which contribute to security problems, directly and indirectly. Sometimes the error is the threat, such as a data entry error or a programming error th...

Data that is transmitted over a LAN should not be altered in an unauthorized manner as a result of that transmission, either by the LAN itself, or by an intruder. LAN users should be able to have a reasonable expectation that the message sent, is received unmodified. A modification occurs when an intentional or unintentional change is made to any part of the message including the contents and addressing information. Messages transmitted over the LAN need to contain some sort of addressing information that reports the sending address of the message and the receiving address of the message (along with other pieces of information). Spoofing of LAN traffic involves: The ability to receive a message by masquerading as the legitimate receiving destination, or Masquerading as the sending machine and sending a message to a destination. To masquerade as a receiving machine, the LAN must be persuaded into believing that the destination address is the legitimate address of the mac...

The disclosure of LAN traffic occurs when someone who is unauthorized reads, or otherwise obtains, information as it is moved through the LAN. LAN traffic can be compromised by listening and capturing traffic transmitted over the LAN transport media (tapping into a network cable, listening to traffic transmitted over the air, misusing a provided network connection by attaching an analysis device, etc.). Many users realize the importance of confidential information when it is stored on their workstations or servers; however, it is also important to maintain that confidentiality as the information travels through the LAN. Information that can be compromised in this way includes system and user names, passwords, electronic mail messages, application data, etc. For example, even though passwords may be in an encrypted form when stored on a system, they can be captured in plaintext as they are sent from a workstation or PC to a file server. Electronic mail message files, which ...

Because LAN users share data and applications, changes to those resources must be controlled. Unauthorized modification of data or software occurs when unauthorized changes (additions, deletions or modifications) are made to a file or program. When undetected modifications to data are present for long periods of time, the modified data may be spread through the LAN, possibly corrupting databases, spreadsheet calculations, and other various application data. This can damage the integrity of most application information. When undetected software changes are made, all system software can become suspect, warranting a thorough review (and perhaps reinstallation) of all related software and applications. These unauthorized changes can be made in simple command programs (for example in PC batch files), in utility programs used on multi-user systems, in major application programs, or any other type of software. They can be made by unauthorized outsiders, as well as those who are ...

One of the benefits of using a LAN is that many resources are readily available to many users, rather than each user having limited dedicated resources. These resources may include file stores, applications, printers, data, etc. However, not all resources need to be made available to each user. To prevent compromising the security of the resource (i.e. corrupting the resource, or lessening the availability of the resource), only those who require the use of the resource should be permitted to utilize that resource. Unauthorized access occurs when a user, legitimate or unauthorized, accesses a resource that the user is not permitted to use. Unauthorized access may occur simply because the access rights assigned to the resource are not assigned properly. However, unauthorized access may also occur because the access control mechanism or the privilege mechanism is not granular enough. In these cases, the only way to grant the user the needed access rights or privileges to pe...

LANs provide file sharing, printer sharing, file storage sharing, etc. Because resources are shared and not used solely by one individual there is need for control of the resources and accountability for use of the resources. Unauthorized LAN access occurs when someone, who is not authorized to use the LAN, gains access to the LAN (usually by acting as a legitimate user of LAN). Three common methods used to gain unauthorized access are password sharing, general password guessing and password capturing. Password sharing allows an unauthorized user to have the LAN access and privileges of a legitimate user; with the legitimate user’s knowledge and acceptance. General password guessing is not a new means of unauthorized access. Password capturing is a process in which a legitimate user unknowingly reveals the user’s login ID and password. This may be done through the use of a trojan horse program that appears to the user as a legitimate login program; however, the trojan hors...

A threat can be any person, object, or event that, if realized, could potentially cause damage to the LAN. Threats can be malicious, such as the intentional modification of sensitive information, or can be accidental, such as an error in a calculation, or the accidental deletion of a file. Threats can also be acts of nature, i.e. flooding, wind, lightning, etc. The immediate damage caused by a threat is referred to as an impact. Vulnerabilities are weaknesses in a LAN that can be exploited by a threat. For example, unauthorized access (the threat) to the LAN could occur by an outsider guessing an obvious password. The vulnerability exploited is the poor password choice made by a user. Reducing or eliminating the vulnerabilities of the LAN can reduce or eliminate the risk of threats to the LAN. For example, a tool that can help users choose robust passwords may reduce the chance that users will utilize poor passwords, and thus reduce the threat of unauthorized LAN access. ...