PC World Article & The Hacker News Article cover the issue in brief. Another site guaranteeing your anonymity and they can't do it. If you are on the web, you are vulnerable. Period. Don't do things you wouldn't want to write home to mom about, unless you are willing to gamble that you and every service you use is better than the hackers of the world.
2015-07-28 edit: Another article on this matter. Gives a method of discreetly finding out who is being discreet. http://motherboard.vice.com/read/who-needs-hackers-you-can-already-see-whos-on-cheating-site-ashleymadison?utm_source=vicenewsfb
Peace, love, & security.
Thanks for reading,