Originally Posted by Stuart C
Although whether you should rely on your AV to detect any viruses depends on whether you have a good AV. Ask Rob. He had an up-to-date copy of Panda and a trojan still got through.
Although in that case, a firewall would not have helped. It may have popped up a query asking if the program should acess the network, but seeing as the program in question was disguised as a speed tester, in all likelyhood, Rob would have answered yes.
A virus has to be run or opened or executed to allow an install like what happened to Kymmy the other day. A firewall is not going to stop that happening it will just flag that the virus is trying to call home. A good virus will disable the firewall and any existing AV meaning you are unprotected due to the running of the Virus.