by David Paul

Created on: November 19, 2008   Last Updated: January 18, 2009

Before everything, you need to recognize that you have an infection and quickly. Some symptoms include: system slowdown, an increase in incoming spam, email being returned to you that you didn't send, strange pop-ups and unusual network or hard drive activity. An obvious symptom of infection is that your anti-malware software caught a trojan.

This is where the "click-and-kill" comes into play. Your software has spotted the trojan, you click "delete" or "quarantine" and it cleans out the trojan. If the anti-malware doesn't find the same trojan or any other infections in the next couple of days, you can breath easy and move on. Otherwise, you may be faced with a deep-seeded and stealthy infection.

One very important item to remember throughout all the clean up process: become informed. Even if you believe you have had a successful click-and-kill, look up the virus by using your favorite web search engine. Find out what the trojan can do and how it likely came to be on your computer. The scariest thing can happen here; there is no trojan found by that name on the internet! Odds are good in this case that your anti-malware application caught the trojan by "heuristics". Heuristics allow anti-malware applications to identify potential viruses before the definitions come to be. If this is the case, find out how to submit that virus to your anti-malware provider for analysis, you may have found a new bug!

A deep-seeded infection will require a series of anti-malware tools to be used. Why? Not all anti-malware applications are perfect. I recently tackled cleaning a trojan infested computer for a colleague, and it took 5 separate applications, each finding a handful of infections before the computer was "clean".

Before you start scanning, use an application like Cleaner to empty out all of your temporary files and folders. Some trojans like to hide out there. In the case of the more serious infections, you will need to disable "System Restore" in Windows XP or Vista. In the worst situations, you need to run all of your scans while in Windows Safe Mode.

The next step is to choose your tools. The set of tools I use: HijackThis!, an anti-adware (like AdAware), an anti-spyware (like Spybot Search and Destroy), an anti-virus (like AVG Free) and a general "anti-malware" (like Malwarebytes Anti-Malware). For more serious infections, if you already have an antivirus program installed, you may want to temporarily install another, clean up your computer, then uninstall one of them.

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