So you've decided to join the infamous group of computer gaming users known as "pirates".
Hey, I've got nothing against piracy to a degree, not everyone has the $$ to hand out for new games. But I won't get into the politics of it all.
Now, you've downloaded a pirated/cracked game (note: crackers are not necessarily pirates themselves, but do tend to blend/work together a lot), and start the install process...... just to get an anti-virus warning pop up. Most users have grown up to take heed of these warnings and delete whatever it is causing the alert. But with cracked/pirated games, this is usually a false-positive.
When games are cracked, certain files are edited, and other code injected to allow the crack to work, and this is what your AV program is detecting.
95% of the time, these alerts can be ignored with no issue at all (and remember to allow/remove from quarantine the file in question or else your game won't work).
The other 5% could very be an actual virus/malware package injected by a 3rd party.
How to avoid this ?
Well, honestly you can't.
Best thing to do, is stick with a single supplier/group that you feel you can trust as much as a pirate can. Check around for popular scene/pirate/cracker groups, especially well established ones. If you can, get access to the "official" (aka private) distribution sites/torrent trackers the group uses rather than 3rd party, where anyone can upload the game AFTER they've injected their own crap into it.
At the end of the day, you're dealing with pirated material and operating in the "underworld", and as with drug dealers, you never quite know what you're getting.....