Let's talk something about viruses/trojans.
Certainly Antivirus(Norton,Kaspersky,NOD32,etc) is very good thing to defend yourself,but we must remember that Antivirus couldn't catch a new virus,because the antivirus laboratory doesn't know its code.
So to defend yourself you need to do the next :
1.Install antivirus and always update it.Once a week scan your system.
2.Install firewall(Outpost,etc).
3.Close ports that you aren't using.
4(main). EDIT INTERNET OPTIONS -> SECURITY -> INTERNET(For example ActiveX control must be always turned off).
5. NEVER!NEVER!NEVER OPEN PROGRAMS LIKE : MONEY DOUBLER,GET MONEY,etc.!!!!