its very possible that someone was able to get into your system and change the firewall password, especially if you had open ports to begin with and whoever penetrated your system simply turned off your firewall then was able to more directly access your computer. i would suggest checking this site out https://grc.com/x/ne.dll?bh0bkyd2
scans your comp for ports and vulnerabilities, definatly helped me lock down my system
-cheers