Have you noticed a sudden slow-down in your PC's performance? Does your Internet router or modem seem to be working (lots of lights flashing) even when you're not browsing the Net? Have your browser settings (like homepage and default search engines) changed without your permission? If you answered 'yes' to any two of these questions, there's a good chance that your computer has been hijacked by hackers. Hijacked PCs are often used to harvest personal information like credit card details and are sometimes even employed by hackers to act as web servers which spread more spam, Trojans and viruses as well as other dangerous or illegal software. But fear not: there are three simple steps you can take to rescue your hijacked computer.
Step one: Disconnect
The first thing you should do is disconnect your PC from the internet and your home network. This is important for two reasons: hijacked computers receive instructions automatically via the internet, as well as uploading private information they may have harvested; also, an infected PC might well infect other devices connected to your home network, spreading the infection and putting more of your data at risk.
Step two: Clean up
You can get your PC clean by downloading and installing various free programs, but as your PC is already offline you'll need to get hold of them at a friend's house or perhaps at work. Make sure that you use a new USB stick or CD-ROM to store the software as any storage device that has been in contact with the hijacked machine is a potential infection hazard. The programs you'll need are: Ad-Aware, Avast! Antivirus, GMER and Spybot Search & Destroy. Install these and run each in turn, using the maximum possible security settings. It's a good idea to run them in Safe Mode too (you can launch Safe Mode by pressing and holding the F8 key as your computer boots).
Step three: Protect yourself
By now you should have eliminated even the most sneaky key-loggers and Trojans from your PC - but you're still at risk if you're not a careful Internet user. Downloading certain pirated materials or software cracks over the net will massively increase the chance that your PC will become hijacked again. The best advice I can offer here is that once you're sure that you've erased all sign of the offending malware from your computer, you should use a backup program to create a one-off copy of your system in a stable state. That way, even if your anti-virus software and anti-spyware precautions somehow fail, you'll have a safe version of your system which you can fall back on.