Ah the old cracks, if you google it every link says that Warning going to the following site may harm your computer the one exception was www.cracksfound.com (aka don't go there it has some link to porn). So Its safe to assume that most cracks have a virus/malicious code attached to it. Take Heroes 5 for example, I have the game and I dowloaded a crack for some reason, then i noticed my firewall requesting that Heroes 5 want access to the internet to some private IP address so just don't get one.
Btw making an iso image from your dvd may not work. There is security on the disks that will not allow you to run it like this. Games like Fifa07, GRAW, NFS:C do not work by making iso's.