Actually, no. The developers put some serious hack-detection stuff in there, so if you pirate it you'll have to face an invincible scorpion monster as soon as you grab the pistol.
Wait! WAT??!!!
AAAAAAAAAAAAAAARRRRRRGGHHH!!
Funny that at the age of 30, when you do not have any financial reason against buying a game you want, you are forced to pirate due to DRM. But come to think of it, it's their loss and not mine. The same stuff happened with Deadrising II, nowhere did the box say it requires constant internet connection. Guess if I now use a cracked or a vanilla version of that game? But at least I bought it, which doesn't seem to happen with Serious Sam III.