I was browsing and came across a rather back-end state-government site that's vulnerable to SQL injection. (Searching for a ' yielded an error, and I toyed around with it until I got a list of tables.)
I know the proper thing to do is to alert the webmaster of the problem, but I've had bad luck simply sending an email. I've done this two times prior. The first time I received a "Thanks" with the problem not being fixed. The second time I got back nothing. I would much prefer the problem fixed, as my own data could potentially be released.
What is the most effective and professional way to tell a third party that their website or software product has a security vulnerability? Especially when you have no professional contact with the company or organization whatsoever?