Anyway, Trojans and backdoors are basically the same thing. Your best bet would be to get Antivirus protection and update it. If you already have a virus/trojan, go into safe mode and try running removal tools for the type of virus you have. Also check and remove spyware while you're at it. Adaware detected Welchia on systems even.
the least you could do is get a decent firewall, then i would invest in a virus scanner that doesnt suck. too bad they dont have software to filter out complete fuckwads