Originally Posted by
raistlin
How do you know, exactly ? Unless you are running a weird operating system where most malware cannot work (say, a customized version of QNX), possibly on customized hardware as well, or unless you never put any media on your machine and never, ever connected it to the Internet, there's no way on Earth you can know your machine is NOT infected.
You can know your machine is not BLATANTLY infected by COMMON malware. Which is a completely different thing than being sure you are not infected at all
You would be surprised at how some things out there are nasty, stealthy and quite good at tricking people into infecting themselve.
But that's the purpose of scanning on a regular basis. I've made the determination that scanning every month or two and confirming what I already believe to be true (i.e. no malware exists on the PC) is sufficient, compared with the (often drastic) overhead of a continually running AV / anti-malware program.
Believe me - the risk of being infected by malware, on a modern OS kept up to date, with a modern browser kept up to date and on a typical LAN connected behind any half decent router running NAT is tiny. I really do mean it - you'd have to go out of your way to end up with malware on the PC.
To
ScottC - interesting point about MSE - I'd looked at it when it first came out and was somewhat sceptical, I may re-visit this though.