This really applies to Wordpress clients, but it’s a warning to all clients.
If your not making your own theme, always download your themes from a reputable site, there are too many sites out there offering hacked or altered themes.
Some people call it linkware, but it’s actually junk.
You can find if the theme has this junk in it, by checking footer.php, functions.php or header.php. There will be a strink of numbers and letters and the words “Base64 Gzip" or something similar.
If your happy to decode the code in these themes, that’s fine. But always remember that any junk code in a theme may not just affect your blog, it might interfere with our server.