My IP address has been banned from the Ubuntu forums for spam but I have no knowledge of the spam or what could be happening. I have been in touch with the admins there but they refuse to help basically saying "We will un-ban you when you stop the spam." Since I don't know what is happening it feels to me like a security problem or maybe a virus on my Ubuntu machine is sending spam? I know people say that Ubuntu is virus proof but could this be an exception?