The FBI and the U.S. Cybersecurity and Infrastructure Security Agency are urging users of popular email services like Gmail and Outlook to be on the lookout for a dangerous and potentially costly ransomware scheme. A bulletin released this week detailed a warning for the Medusa ransomware gang, a group that’s been active since 2021.

The FBI has issued a warning about ransomware threats targeting the United States Postal Service and Gmail and Outlook users. According to the agency, the Medusa ransomware gang—an organization that has been active since 2022—is behind the attacks.

The Federal Bureau of Criminal Investigation along with the Cybersecurity Infrastructure Security Agency and the Multi-State Information Sharing and Analysis Center are warning of a new phishing campaign by Medusa ransomware operators targeting email users to gain network access.