These are open source products, and it's nearly a criteria to put that at the top of the download, When you buy software that line is in its the terms and condition's that you agree to. If you read them

But to be on the safe side always make backups on your machine and your databases.

Then test on your local machine before installing to the net,(yes I've learn the hard way).

But if there was a problem with the program I'm sure the zen Cart community would have it sorted out quickly