The footer link is not the least bit malicious -- it is very common to put a backlink into a FREELY distributed product, and most users of open source applications understand that the link should be left in as a courtesy to the developer whose hard work has provided them with an excellent tool.
I have no doubt that once you have spent a little time exploring the other free themes available for WordPress that you will quickly realize what an incredibly robust product Atahualpa is by comparison - as far as I have found it does not have an equal in the free theme world for the level of customization and control it gives you.
An unobtrusive backlink is a small price to pay. Or you can make a token donation to the developer and receive the detailed instructions for removing the link from all of your Atahualpa installations.
Update: After posting I had a look at your history on the forum and see that you have been posting for 6-8 months (so I assume you have been using Atahualpa for an equal amount of time). The courtesy footer links have been a part of Atahualpa since at least January (which was when I started using it) and you made a post in March
http://forum.bytesforall.com/showthread.php?t=700 politely inquiring as to how to remove it -- so I guess it just seems odd that all of a sudden you are bothered and distrustful of an innocent and well-earned footer backlink!