Hey everyone, Theme Lab is actually my site. I just wanted to clarify that there never has and never will be any themes hosted on my site with obfuscated code to hide ad links or other malicious things. Thanks to the moderators and original poster for helping clarify that this theme wasn't actually downloaded from my site.
Unfortunately I really can't control if someone takes a theme from my site, puts it on their own site and embeds their own obfuscated ad code in it, which is what happened in this case.
I'd recommend downloading free themes only from the WordPress.org theme directory and other trusted sources. If you search "wordpress themes" in Google and find a theme that way, chances are it will have encrypted code hiding several sponsored links that probably weren't there in the original theme.
Just to be on the safe side, you should probably run all themes you get from other sites through a plugin called Theme Authenticity Checker which automatically checks for encrypted code and displays any outgoing links.
I've written about the issue in this post: Stop Downloading WordPress Themes from Shady Sites.
Also to the original poster, feel free to download a fresh copy of the WP Multiflex 5 theme if you don't feel like messing with encrypted code.