That is some seriously obfuscated crap.
Looks like a hack to me: http://www.google.com/search?q=eval%28base64_decode%28
Paste the whole string of code into Google for more specific results.
FAQ: My Site Was Hacked
I guess it could be some obnoxious attempt by a theme author to make sure a piece of code stays in the footer, but with obfuscation like that I wouldn’t trust the theme.
Moderator
Jan Dembowski
(@jdembowski)
Forum Moderator and Brute Squad
That obfuscated nonsense is from some Very Bad People™.
You should consider selecting a different theme from a reputable source, that provider is doing something dodgy and all you’re doing is getting them ad revenue from your blog.
http://wordpress.org/extend/themes/