(Reuters) - The U.S. government on Thursday warned computer users to beware of fake emails they may receive from hackers claiming to be from the Department of Homeland Security and demanding money to reinstate use of their computer.

Homeland Security's U.S. Computer Emergency Readiness Team, or US-CERT, published an alert on its website warning it had received reports of DHS-themed "ransomware."

"Users who are being targeted by the ransomware receive an email message claiming that use of their computer has been suspended and that the user must pay a fine to unblock it," the warning said, adding that the ransomware falsely claims to be from the department and its National Cyber Security Division.

Ransomware is increasingly widespread malicious software that purports to encrypt a user's files and then demands payment to unlock them.

US-CERT urged users and systems administrations to use caution if they find a questionable email message that could contain the ransomware. It said to urge users not to click on the messages or submit any information to Web pages.

(Reporting by Deborah Charles; Editing by Doina Chiacu)