Windows 7 is as reliable as Linux although it does suffer more from fragmentation and there are a lot more poorly written apps for Windows not to mention it suffers from it's own success. If Linux was as popular as Windows then it would have as many if not more security attacks by unemployed teenagers as well.

Linux is secure, but don't assume it's secure. You could be one click away from disaster.

I've only ever had one virus in Windows and that was because I was looking into hacking when I was an unemployed teenager. Security is about common sense more than anything. If I had a virus in Linux I'd never know as most are not destructive they sit there logging your passwords without you knowing. I don't run a virus checker. Windows viruses can't infect Linux though.