All hackers look like this. Flickr/Brian Klug Millions of Ashley Madison customers had their personal information leaked in a hack of the site, and now blackmailers are making big money using the data.

The Register reports that researchers have been able to track payments online that were sent using the virtual currency bitcoin.

Cloudmark analyst Toshiro Nishimura looked into bitcoin addresses that were included in emails sent to victims of the Ashley Madison hack. Blackmailers have been contacting users of the site promising to remove their data from the internet, or threatening to send it to their relatives or colleagues.

If you know a bitcoin address then it's possible to track payments sent over the internet to it. Nishimura found several bitcoin addresses that were being used by blackmailers to seek payment. He was able to track payments to the addresses, and found 67 different transactions indicating that Ashley Madison customers paid around $6,400 to scammers.

Toronto Police held a press conference in August to outline the investigation into the Ashley Madison hack. During the press conference, police showed an example of one of the blackmail emails received by an Ashley Madison customer.

There's a big opportunity for blackmailers to make money using the leaked Ashley Madison customer emails. There are 32 million account holders on the database. If a blackmailer emailed all of them, but only 0.01% of users paid up, then the blackmailer could still earn $1.4 million (£900,000).