Identity Crisis

We recently found a website with some awesome wordpress themes and we immediatley went and put them on our sites.  However, a little later I discovered that the footer.php file was encrypted, apparantly to stop people changing the links in it.  Now that is all very well but how do I know what else is in there?  I did a search of the net to try and find a way to decrypt and discovered that some encrypted footers had been used to hide malicious code.  There were some instructions on how to decrypt the file but I was not successful so these beautiful themes will have to go back where they came from.