Verifone is checking into a breach of its computer network, reports security blogger Brian Krebs.

Krebs' report includes an image of an internal email Verifone sent to staff and contractors dated Jan 23, 2017, warning them to change their passwords within 24 hours, and barring staff from installing software on company computers.

The memo, attributed to Verifone senior vice president and CIO Steven Horan, says Verifone is investigating an IT control matter and it is taking steps to improve those controls.

Verifone also told Krebs the intrusion was in a limited portion of its internal network and did not impact its payments service network. The processor did not tell Krebs how it learned of the breach. An unnamed source told Krebs Verifone was notified by Mastercard and Visa of the potential intrusion, which could have happened as early as 2016.

Later on Tuesday afternoon, Verifone told Krebs the hack was limited to about two dozen gas stations. The terminals remain operational, the company told Krebs.

Verifone did not immediately return a request for comment.