Your computer may be infected with a virus that infects files you download. Virus scanners do not and can not detect every virus. Just because the virus scanner 'removes' it doesn't mean it's necessarily gone, as well. Additionally, your scanner may be giving a 'false positive'. This means that it's reading a file as a virus when it actually is not one, and is perfectly fine.
As a note, I personally do not use any form of live-scanning virus scanner, and I have remained virus/trojan/malware/adware (not including tracking cookies)/etc-free for over seven years (exception to intentional infections on virtual machines).
As far as my knowledge goes, there are no viruses/trojans posted on the Blockland forums. If there are any, report them to Badspot immediately. That stuff does not belong here.
How do you know if u have a virus if u don't have a virus program? :P
Using tools that can show you processes and the threads/strings being used by them, observing program behavior, monitoring inbound/outbound bandwidth to and from your machine, and checking your startup list usually.
