Stu several points here
In the world of the internet plagiarising is rife Even Tory Blair did it
Talking to friends who lecture at Unis, it's a very big problem. One even found half an essay cut and pasted from a mate's obscure paper published a few year previous. Student swore him blind it was his own work. My mate phoned his mate up and handed the phone to the said student on speakerphone. The true author tied him up in knots on the analysis/results, as thick git couldn't remember them. Oops! Lost the whole assignment and failed the module for that year.
Matt asked did you copyright it? The simplest way to do this is sign and date all original work. And keep them in hardcopies.
Don't delete e-mails sent with such docs on them.
However, unless you're moneybags and you can afford to go to court to establish your ownership, you have very little recourse if some thieving scum nicks your work.
Sad, but that's the way of the world.
You could try asking the site to take down the thieves work, citing your work on FM and pointing to the the dates and the similarities in his work to yours.
If they say no, then the only thing realistically you have left is to expose them on this internet thingy.
On the other hand you could take it as a form of flattery as it was that "good" that a thicko felt he needed to copy it and pass it off as his own.
An honorable person would have asked you could he use it in his review with credit to you as the originator.
