hum well a trojan can do that kinda stuff but... why would it? Most trojans are used to get into someones computer and use it for storage space or as a online server. so they stick files on your computer and use your bandwidth so other people download from you. not normaly something done to personal computers. Most people that say stuff like this happening to them just say it because they downloaded it themself and were caught with it and dont want to look like a total pervert/pedofile/necrophyiliac/homosexual or whatever depending on what they were caught with that they dont want to admit to enjoying. But it is totaly possable toget a virus that would do it.
If i was them i would run a couple antivirus programs and a few anti spyware programs. then install a firewall. Hardware firewall is best but software firewalls help too.
a couple decent free online antivirus programs worth running.
http://housecall.trendmicro.com
http://www.pandasoftware.com/activescan
Antispyware stuff also free also worth running.
http://www.lavasoftusa.com/software/adaware/
http://www.safer-networking.org/en/download/
After running that stuff they should install a firewall like zone alarm. its free for the basic firewall and one of the best out. just takes a little time to set it up.
http://www.zonelabs.com/store/conten...eeDownload.jsp
After that they should Hit control alt delete to get the windows task manager up. hit the processes tab and start looking up all of those things on google. thats every program thats running on your computer. if theres a virus active on it still after all that antivirus stuff it will be there hidden somewhere. most viruses are named something that is innocent looking and trys to hide as something that belongs there. so if you see like aol on there and you know you dont have aol on your computer its a good chance that is a virus.
After doing all that annoying pain in the butt stuff. go to windows update and update windows over and over again till it dosnt download anything new. They patch all sorts of security holes all the time so the more updated you are the safter your computer is.
After all of that it should be virus free and running happy without any extra porn sneaking in that dosnt belong there. so... get your friend a subscription to some fat bald ugly and over 50 porn magazine. That way they dont go threw any porn withdrawl symptoms.