Is that a virus, or a malfunction?

You might have a virus if..." A virus infection could also cause some of the following symptoms. Keep in mind that these symptoms are also typical of ordinary Windows system problems, so you'd have to run a complete virus scan (with updated definitions) before you could definitively diagnose a virus.

Windows will not start at all, even though the user has made no system changes, installed or removed any programs, or made any registry edits since the last time it started successfully.
Windows will not start because certain critical system files are missing (and you see an error message listing those files), and the user is confident that he or she did not accidentally delete them.
The PC starts up normally sometimes, but at other times will hang before the desktop icons and taskbar appear.
The PC runs very slowly and/or takes a long time to start up.
Out-of-memory error messages appear, even though the PC has plenty of RAM.
Viewing the system processes via Task Manager shows that an unknown process is consuming a high percentage of the CPU time.
From the Task Manager view, you notice programs or processes running that you do not recognize, even after shutting down all running programs and system tray utilities.
New applications will not install properly.
Windows spontaneously reboots for no apparent reason.
Applications that used to run normally are now crashing frequently. Removing and reinstalling them does not solve the problem.
A disk utility such as Scandisk reports multiple serious disk errors.
A partition completely disappears.

The key to distinguishing virus-related system problems from ordinary ones is often situational. What did the user do right before the problem started? It never hurts to ask. If possible, check the user's e-mail box to see whether an e-mail containing a virus might still be hanging around there. Check his or her Deleted Items, and check the Sent Items folder as well to see if the virus may have been spread to others. For definitive virus detection, you must turn to an antivirus program with updated definitions. If a reputable antivirus program will install, run, and complete a check successfully, and if its definitions have been updated within the last 24 hours, you can be fairly confident that the problem is not a virus. Otherwise, virus infection is still a credible suspect. Are the definitions up to date? Most antivirus programs can't detect viruses that they don't know about. There are exceptions, such as programs that monitor the file sizes and dates of essential system files and warn you if they are about to be changed. However, the vast majority of threats circulating today are not true viruses because they do not actively infect your existing .exe files or boot sector. Instead, they are Trojan horses, back door programs, or worms, whose behaviours won't normally trigger that kind of proactive detection. Therefore, updated definition files are your only reliable line of defense against new virus threats. Norton AntiVirus, for example, checks for new definitions on the company's server and installs them automatically. Be warned, however, that some services (such as Symantec's Live Update) update their servers only once a week except during peak periods of virus problems, so you might not always get the latest updates by running Live Update. Going manually to the company's Web site and comparing the date of the most recently posted definitions to the date shown in your software is one way to ensure you have the latest stuff, but that can be a little taxing. Symantec offers an Intelligent Updater service that updates virus definitions every business day, which is a great alternative for administrators with mission-critical PCs to support. Tip -- dealing with Klez If you think you might have a W32.Klez.mm virus or a variant thereof, you'll need to download and run a special Klez removal tool. Symantec offers a free one on its Security Response Web site, where you can also view a list of removal tools for many other specific viruses. Do a full system scan Assuming your virus definitions are up to date, you can be reasonably certain that if an antivirus program successfully completes a full system scan and tells you there is no virus, there probably is no virus. If you remain skeptical, check one of the major virus security Web sites after 24 hours; it's possible that a brand-new variant has slipped in. If that's the case, other people should be reporting it and it should be all over the virus community's news within 24 hours. If your antivirus program won't run or won't do a full system scan, or if you buy a new copy and it won't install, this is a significant sign there is a virus infection. For example, many varieties of the W32.Klez.mm mass-mailing worm include commands that disable your antivirus software and make it difficult or impossible to install new antivirus software. Unfortunately, there's no simple magic formula for determining whether a virus is the source of PC problems. Many virus symptoms are identical to the symptoms of normal system problems. The guidelines above, however, can help you make an educated guess.

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