You can sit around speculating about "is this a virus or not?" all day long, but for a definitive answer, you must turn to an antivirus program with updated definitions. If a reputable antivirus program will complete a check successfully, and if its definitions have been updated within the last 24 hours, you can be fairly confident that there's no virus. Otherwise, virus infection is still a credible suspect.

Dealing with the Immediate Threat

Now here's the catch-22: If you do not have an antivirus program already installed, you should not install one if you suspect a virus infection. Don't laugh -- it's true! The main reason is that many viruses disable antivirus software or prevent programs from being installed, so it probably won't work right if you install it with a virus present.

"So what do you expect me to do?" you're probably thinking.

Well, there are some workarounds. One of them is that Symantec provides free removal tools for individual viruses, as shown in Figure 4-1, so if you know you have a particular virus (for example, if you got an email from someone saying you sent them an infected message), you can download a removal tool for it and run that.

Figure 4-1: Symantec free removal tools.

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You can also use free web-based virus scanning tools. For example, McAfee offers one called Free Scan at their website, as shown in Figure 4-2. You have to register to use it. It won't remove viruses, but it will tell you definitively whether you're already infected. If you're not, then you can install antivirus software with confidence.

Figure 4-2: McAfee lets you check for viruses via the web.

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Another workaround is that the newest versions of some antivirus software (such as Norton Antivirus, also from Symantec) have a preinstallation virus check so that it can verify your system's virus-free status before it's installed.

Yet another workaround is that if your antivirus software is already installed but not updated, you can usually download an update for it and run a complete system check even if you have a virus. The viruses that disable your antivirus software typically only disable the automatic checking process, so you can still do manual scans.