...Anything on your website becomes Intellectual Property of the site owner once it has been posted to the internet. If you can track down the persons responsible for the destruction of your site to a certainty of who it is and are able to identify them. Then you can take legal action against them.

Known and Willful Destruction of a persons Intellectual Property in reference to Internet Copyright Laws is a federal offense...

...Lookup the US and International Laws regarding Hackers, Internet/Network Security, US Internet Security Laws and Intellectual Property. The US Library of Congress has a good amount of info on both. (http://www.copyright.gov/resces.html)

...You are not required to register your copyright with the US LOC for it to be a legal copyright when in reguards to Web Sites. All Registering a Copyright does for you is have it on record so that if you ever have to sue or get sued for using certain content, you will have a federal statement of copyright recognition to present as evidence of your right to own such content. Further, it allows you use the copyright symbol, which your not supposed to do if you haven't registered the copyright.