If you wanna check that AVAST is doing it's job, run a trusted third-party anti-malware program like good-old free version of Spybot S&D over at Safernetworking.org. It's free, it's trusted by IT professionals, and it just works. But even it can't defend you if the fault lays between the chair and the keyboard: If you get tricked into downloading and installing a piece of malware, ignore all the red flags that Avsat, Windows and common sense throw up... well what can I say; Sad day for you.