The only vulnerability that we have is from robots mass registering. I disabled the protection (a random numbered image that new members must input at time of registration) because most people would be confused.
The first such attack that I will get from a robot, I will delete those registrations and put up those shields.
The other vulnerability which was causing the site to be down all the time was an attack coming in from the contact form. They were using it to mass mail thousands of mail, drawing all the server ressources and causing a crash. The most severe crash was when the data got corrupted and we lost 6 weeks of postings three or four months ago. I closed that loophole by requiring non members to fill in the numbers from a random image. It has been 3 weeks now since the site has not been down.