Personally, I don't care where you got the software. It's not my job to police you.
Regardless of the version you are using, legal, illegal, whatever - if it used to work fine and now the performance is slowly changing, I doubt the OS is the problem. But you never know, I guess. But plenty of people with purchased copies have had some pretty strange problems, too.
Wouldn't a firewall stop the typical backdoor? My hardware firewall won't let anyone access my network from the internet, and ZoneAlarm won't let any application or process access the internet from my network without my permission. Or am I missing something?