Flickr/jseliger2
There are now numerous websites popping up that promise to let you see if you've been affected by the hack. You enter your email address, and the site checks if it's in the data dump.
One of these is HaveIBeenPwned.com. It sets itself apart from other similar services by not just checking the Ashley Madison database, but also cross-referencing it with a huge archive of previously hacked customer details.
This includes the Adobe hack, which affected a staggering 150 million accounts, as well as a Snapchat hack affecting 4.6 million accounts, and an Adult Friend Finder hack affecting 3.9 million accounts. Altogether, the site can check your email against 220 million potentially compromised accounts drawn from 53 hacked websites.
Troy Hunt, the developer behind HaveIBeenPwned.com, has set the Ashley Madison data so that users will only receive an email if they've been hacked. This means you can't use the website to see if your friends or co-workers have been affected. In a blog post, he explains that he has done this because he doesn't "believe it's responsible to make all the AM accounts discoverable by anyone" because the data is "sensitive."
It's also worth checking even if you have never signed up for Ashley Madison yourself. The site doesn't actually verify the email addresses users provide, so it's easy to sign up with a fake address, or one belonging to someone else. You could be in there without even realising it.
Here's how the site looks:
HaveIBeenPwned.com