I spent five hours last night cleaning an obnoxious malware called 'System Tool' from a friend's brand new laptop. Now, even though Best Buy had put some crappy antivirus on there
and I gave her a list of what programs to download to protect her computer, which she didn't, she managed to acquire it.
Oh, it did blue screen/memory dump when I tried ctrl/alt/del.
I browse with Chrome and set it to block pop-ups. I run with Spybot S&D, AVG Free, Ad-Aware, and Malwarebytes. They use very little system resources and I have never had anything get by them.