SECURITY ISSUES? I got hacked

Hi all,

So a user of my website told me that when they tried to login, they saw a warning from their AVG saying my website contained malicious code, etc.

The warning was a BlackHole Exploit ...

I installed AntiVirus plugin and it scanned my theme files. It found the malicious code:

eval(base64_decode ....

on the first line of various FrameMarket theme and some on the file theme I created. I have no idea if this has to do with the theme itself or how it happened.

Any help would be greatly appreciated!!! How can I check plugin files? What plugin is good for security measures. What next steps should I take?

My website is http://www.ourhoneymoongiftregistry.com

Thank you,
Giovanni