Chances are a worm or trojan got in and the computer is hijacked. The only solution to this: complete wipe of the hard drive, reinstallation of the operating system, and then finding out a good firewall (Zone Alarm is a good free choice) as well as an antivirus program (good one to try, AVG which offers a free option). After those two things (they are the FIRST things that should be done before redownloading and reinstalling anything else), make sure the latest definitions for the antivirus are downloaded and installed. Then locate and install anti-malware software (Spybot and Malware Bytes are good options and free). Try not to use Internet Explorer as browser.
Do not redownload anything until all of the security software is up and running.
It may be a good idea to use an OS that is legit ... a bootleg copy may be a reason why something managed to sneak into the system and completely mess it up. I don't know what OS he's using.
I'd suggest that you both spend time learning about online security and the issues we all, as users, have to face every time we go online. Even with the best of security suites available installed, we all still run certain risks, and as a gamer, the risks increase at least 50% (I am a MMO gamer). If certain sites are visited (porn sites, as mentioned) the risks go up 100% every time you log on to one, browser hijacking being among the most common.
Social networks like FB and MySpace also present risks. I've had my browser hijacked via one of those stupid app games in FB. I don't use apps there any longer for that reason.
Emails is another way by which a system can be hijacked (even without the user's knowledge). All you need is open an infected email or attachment, a worm/trojan sneaks in, and there it goes, zombie machine in the making (particularly if you keep it logged to the internet 24/7 and never bother to turn the system off).
Good luck.