Ashley Madison, an online extramarital dating service that claims to protect users' privacy and security, has had its customer database compromised.

A hacker group that reportedly calls itself The Impact Team ostensibly stole financial records, card data, customer information databases, source code repositories, emails and other proprietary information from the site's parent company Avid Life Media. Brian Krebs, the former Washington Post staffer who now blogs on cybercrime and online security, first reported the hack last Wednesday.

The site has now been secured and the unauthorized access points closed, according to a Monday statement by ALM addressing the breach.

"We were recently made aware of an attempt by an unauthorized party to gain access to our systems," it said. "We immediately launched a thorough investigation utilizing leading forensics experts and other security professionals to determine the origin, nature, and scope of this incident."

ALM is working with law enforcement agencies to investigate the cyber-attack and intends to hold the offenders responsible, it added.

Ashley Madison has more than 37 million users. The hackers also compromised data from sister sites Cougar Life and Established Men.