The shraring of product keys, serials, cracks, warez, etc is piracy and therefore illegal according to the laws in just above every modernized country. Depending on how much you pirate the penalty could range from a very hefty fine (tens of thosands of dollars) to a prison term. For that reason alone I'd stay away, oping instead to by the small cost of the software from a legal source.
Aside from that, your friend is right...most of those sites and downloads are loaded with malware, and to top it off the cracks can frequently cause seurity issues with the software.
The reason the sites are still around is that most of them are fly-by-night...the authorities track them down, so they shut down, move elsewhere, and start again. They also hide in countries where the laws are not as stract, buying them more time before they have to cut bait and run.
The same goes for downloading copyrighted software and music using torrents and P2P software...downloading copyrighted content is illegal and you run a high risk of a massive infection in the process.
In short, STAY AWAY.
do the serial codes and cracks really work , i never tried it coz one of my frend told me that those types of sites contains viruses, worms, trojans and all kind of stuffs that can make ur computer in doom. is it real that those sites are spreaded with viruses, if so why r they doin so. if those are carrying so much viruses and stuffs do they cant be banned by anyone?