I hear ya and you have my condolences on the initial shock and outrage. And good luck with Yahoo and other major sites. You'll have to prove, often with notorized documents mailed, faxed or scanned and emailed to them before they'll consider any action. Which is understandable given that anyone can claim a work as their own putting the onus of disproving their claim on the original author. Forums are a bit easier, while owned sites are a tossup, since in some cases, such as blogs and homepages, eventually you'll have to contact the site owner, which brings you back to verifying through a paper trail that you're the original author.