If the answer to the question, "Has your computer ever been infected?" is "yes", the odds are most likely that you, along with countless thousands, received help at one of the many security forums.
There are any number of tools available for analysts to use to determine the nature of the computer infection as well as a variety of tools. However, there is one common software that stands out above the rest. That software is HijackThis, developed by Merijn Bellekom. Gain some insight on what prompted Merijn to create HijackThis and what he is doing now in a recent interviewed by Michael Simpson at PCS Suite 101.
If you have been helped at one of the security forums through the use of HijackThis, consider sending Merijn a small donation.
Hat Tip: plodr at Freedomlist.