Adware is software that displays advertisements on your computer. These are ads that inexplicably pop up on your display screen, even if you're not browsing the Internet. Some companies provide "free" software in exchange for advertising on your display. It's how they make their money.

Spyware is software that sends your personal information to a third party without your permission or knowledge. This can include information about Web sites you visit or something more sensitive like your user name and password. Unscrupulous companies often use this data to send you unsolicited targeted advertisements.

I've noticed more postings in the Microsoft Windows XP newsgroups about these threats. Many of the postings ask how they can tell if they have spyware on their systems and how to remove spyware if they find it. A small handful asks how to fix problems left over after removing spyware. I'm glad to see a lot of the advice offered from other enthusiasts and I'm going to share some of that advice with you in this month's column.

The Microsoft Windows Malicious Software Removal Tool checks computers running Windows Vista, Windows XP, Windows 2000, and Windows Server 2003 for infections by specific, prevalent malicious software including Blaster, Sasser, and Mydoom and helps remove any infection found. When the detection and removal process is complete, the tool displays a report describing the outcome, including which, if any, malicious software was detected and removed.

Microsoft releases an updated version of this tool on the second Tuesday of each month, and as needed to respond to security incidents. The tool is available from Microsoft Update, Windows Update and the Microsoft Download Center.

Spyware Information

Spyware information is available in abundance on the Internet, but web-surfers often find that there is so much information it is difficult to get a straight answer out of any online site. If you need spyware information, you have come to the right place. At Sunbelt Software, we know spyware inside and out because we are constantly working on ways to find it, remove it, and keep it from spreading.

Computer security imposes requirements on computers that are different from most system requirements because they often take the form of constraints on what computers are not supposed to do. This makes computer security particularly challenging because we find it hard enough just to make computer programs just do everything they are designed to do correctly. Furthermore, negative requirements are deceptively complicated to satisfy and require exhaustive testing to verify, which is impractical for most computer programs. Computer security provides a technical strategy to convert negative requirements to positive enforceable rules. For this reason, computer security is often more technical and mathematical than some computer science fields.

Typical approaches to computer security can include the following:

• Physically limit access to computers to only those who will not compromise security.

• Hardware mechanisms that impose rules on computer programs, thus avoiding depending the computer programs for computer security.

• Operating system mechanisms that impose rules on programs to avoid trusting computer programs.

• Programming strategies to make computer programs dependable and resist subversion.