One of the more esoteric but dangerous pieces of malware that might infect you is a rootkit. This software uses tricky techniques to shield itself from many anti-spyware, anti-malware, and anti-virus programs. A rootkit hides deep in your system, and allows someone to take complete control of your PC without your knowledge. Rootkits typically are spread online in a variety of ways, such as riding along on another download.

Some anti-virus tools, such as Avast, claim to detect and kill rootkits. Many don't. But even if you are using an anti-virus tool that claims to detect them, you can't be too safe. So you'd do well to download, install, and use F-Secure Blacklight Rootkit Eliminator, a freebie designed to do one thing, and one thing alone: detect and kill rootkits.

The program looks inside your PC's folders, files, and hidden processes, looking for signs that you've been infected with a rootkit. It then tells you whether your system is rootkit-free, or possibly infected. It lists every possible sign of infection. Double-click on every one of them, and you'll be shown more information, such as a description, the company that made it, the file location, and so on. You can then use Blacklight Rootkit Eliminator to get rid of the threat, by renaming the file and giving it a .ren extension so that it can't do any further damage. However, before taking that step, it's a good idea to search for the file name on Google and make sure that the file truly is a rootkit, and not a legitimate file. If your PC continues to function well after you've renamed the file, you can eventually delete the renamed files.

Note that if you're not experienced, you might want to stay away from this program. Renaming and deleting files could possibly wreak havoc on a PC, so if you're not comfortable renaming, restoring, and deleting files--and troubleshooting PCs--you may be courting danger.

--Preston Gralla