POPULAR social media network Reddit said tonight a hacker had broken into its systems and accessed users' data - including email addresses and encrypted passwords.

The site revealed it has discovered a computer attacker had compromised a few of its employees' accounts in mid June.

2 Email addresses and passwords have been compromised Credit: Getty - Contributor

A copy of an old database backup containing very early Reddit user data from the site's launch in 2005 through May 2007 was accessed by the hacker, the network said.

"Although this was a serious attack, the attacker did not gain write access to Reddit systems; they gained read-only access to some systems that contained backup data, source code and other logs," said Reddit's founding engineer Christopher Slowe.

"They were not able to alter Reddit information, and we have taken steps since the event to further lock down and rotate all production secrets and API keys, and to enhance our logging and monitoring systems.

"Now that we've concluded our investigation sufficiently to understand the impact, we want to share what we know, how it may impact you, and what we've done to protect us and you from this kind of attack in the future."

2 A copy of an old database backup containing very early Reddit user data was accessed Credit: Getty - Contributor

It continues: "Already having our primary access points for code and infrastructure behind strong authentication requiring two factor authentication (2FA), we learned that SMS-based authentication is not nearly as secure as we would hope, and the main attack was via SMS intercept."

Reddit is an American news and content website where registered members submit content such as links, text posts, and images, which are then voted up or down by other members.

Posts are organised by subject into user-created boards called "subreddits", which cover a variety of topics including news, science, movies, video games, music, books, fitness, food, and image-sharing.

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Reddit is now sending a message to all affected users and resetting passwords on accounts where they might still be valid.

Users who signed up for the social networking site after 2007 are clear.

The company has now urged users to check their private messages as it will soon be notifying all those affected.