It’s a Slack Hack Attack. Slack, the popular group chat tool that boasts 500,000 users, has admitted that its database has been hacked and users’ profile information may have been leaked — including sensitive info like logins, email address, and even phone numbers.

Slack had been using a hashing technique to protect the passwords, and thus the hackers were unlikely to have been able to decrypt those passwords. Also, there was no leak of financial or payment information, according to a Computer World report.

The company said that hackers gained access and held that access for about four days back in February. Slack said it has since made some changes to prevent future attacks.

A small number of users who had some suspicious activity in their accounts have been contact. The company also reached out to people whose messages may have been accessed, although Slack did not reveal how many users had been affected.

Slack is adding a two-factor authentication feature to help improve security. It would require users to enter a verification code in addition to their password in order to sign in. The feature is not required, but Slack is advising its users to protect their accounts by turning it on.

Slack is a team communication tool that was founded by Steward Butterfield, a Canadian entrepreneur who is best known for being co-founder of the photo-sharing site Flickr. Slick was launched in August 2013 and signed up 8,000 customers just 24 hours after it had launched.

The company raised $160 million with investors in March 2015, placing the value of the company at $2.76 billion. That’s a big jump from its $1.2 billion valuation back in October 2014, when it raised $120 million in venture capital. It first raised about $43 million in April 2014.