Xfinity is notifying customers of a “data security incident” it says resulted in the theft of customer information, including usernames, passwords, contact information, and more. In a notice on Monday, Xfinity says “there was unauthorized access” to its systems from October 16th to October 19th, 2023.

Xfinity traces the breach to a security vulnerability disclosed by cloud computing company Citrix, which began alerting customers of a flaw in software Xfinity and other companies use on October 10th. While Xfinity says it patched the security hole, it later uncovered suspicious activity on its internal systems “that was concluded to be a result of this vulnerability.”

The hack resulted in the theft of customer usernames and hashed passwords, according to Xfinity’s notice. Meanwhile, “some customers” may have had their names, contact information, last four digits of their social security numbers, dates of birth, and / or secret questions and answers exposed. Xfinity has notified federal law enforcement about the incident and says “data analysis is continuing.”

We still don’t know how many users were affected by the breach. Xfinity will automatically ask customers to change their passwords the next time they log in to their accounts, and it’s also encouraging users to turn on two-factor authentication.

“We are not aware of any customer data being leaked anywhere, nor of any attacks on our customers,” Xfinity spokesperson Joel Shadle says in an emailed statement to The Verge. “We take the responsibility to protect our customers very seriously and have our cybersecurity team monitoring 24×7.”

You can find the full notice, including contact information for the company’s incident response team, on Xfinity’s website.

Update December 18th, 6:37PM ET: Added a statement from Xfinity.