A UK cybersecurity watchdog has issued a warning about new bitcoin ransomware attacks disguised as messages from several government agencies.

According to the National Fraud Intelligence Bureau (NFIB), unknown parties have been reported spoofing emails from the UK Home Office and Ministry of Justice, as well as from domestic energy giant British Gas.

The emails are being used to distribute TorrentLocker, one of a number of malware variants that, when activated, lock up a user's files unless a ransom in bitcoin is paid. A report last year found that the vast majority of TorrentLocker victims opt not to pay.

The NFIB indicated that malicious attachments as well as links to websites are being used to distributed the ransomware. In some instances, affected users are being prompted to fill in a captcha code after being warned about bills or unspecified legal action.

The notice further advised potential victims to back up their data and to report any incidents to cybercrime authorities.

Security lock on keyboard image via Shutterstock