yes. most porn sites, and regular sites in general, will download spyware inot your PC. Spyware isnt what most people think. they dont take private info and use it to hurt you. they monitor the types of sites you go to and use that to pop up certian types of ads.
here are some crutial and
FREE things taht ALL people should have runing on thier computers.
AVG Anti-Virus Free Anti Virus Software
Zone AlarmFree Firewall Protections
Ad Aware Free Spyware Removal
Spybot Search and Destroy Free Spyware Removal
i am willing to bet that if you get one of these spyware removal programs, run it and delete all the crap it finds, it will speed up your PC significantly.