Windows is actually the worst choice of OS for security, especially if you do not have Anti Virus. Next time, move a portion of your coins to cold storage so it cannot be stolen.
what if i told you i run win7 on a comp with about 30 different wallets; no antivirus, no firewall, no nothing.
last time i did a reinstall was 2.5 years ago, and was never infected.
all it takes is common sence, and u will never pick up infection (unless there realy is a zero-day exploit lol)