If you wanted to be really cautious, you could diff the original and cracked binaries and reverse engineer the difference. We did that on a project for a client once (a major software corporation) and the cracked version of their software literally just had one opcode replaced.

The fellow working on the project with me had a lot of specialized domain experience in such things, and told me the actual cracking teams would never put malware in their own cracks, because it would ruin their reputation in the scene.

I'm sure some cracks have had malware added after release by other people, of course, but I wonder how much of it was fearmongering by software companies.