Have a look at http://www.trojanremovers.info/
Now let's also be frank in that most websites offering the supposed best free antivirus software will on most occasions only provide a link to a piece of software that can offer a comprehensive free scan, but will kindly ask for remuneration to fix the problems. Let me say right now that this should never put you off and this is simply because most paid programs are very good in terms of stability and functionality. Without mentioning names it's a fact today that loads of supposed best free antivirus software tools are rogue meaning that once installed onto a PC they inflict harm and won't cure it. So know you would probably want to know how you can find the good ones and avoid the bad ones. Just do some research on reviews and you will find answers but as explained above sometimes paid tools are more worthwhile and I'll explain why below.
If you are after solid 24 hour customer support, a tool that offers free updates, ease of use and extreme effectiveness in removing infections then you might want to choose paid. Just have a quick look at http://www.trojanremovers.info/
Now anyway, the virus as an infection is able to undergo self replication, can spread quickly and one in CPU memory it can prey on and infect other applications that you might open up. They are known to be the more destructive type of infection primarily because they can do a great deal of damage to system contents and possess the ability to open more pathways for further harmful content to attack a PC.