The Office of the Data Protection Authority says a series of fake telecoms bills are being sent to islanders.
The ODPA says scammers, claiming to be from Sure, are targeting older CWGSY email accounts.
They mimic the legitimate billing template 'quite convincingly', and prompt users to click on a link to view their bill online - but this takes them to a fake payment portal or downloads malware.
Bailiwick Data Protection Commissioner Brent Homan says islanders should be vigilant and look out for friends or family who are less tech-literate.
“Email phishing attempts from fraudsters spoofing legitimate service providers are a common tactic used to steal your data and money.
“Pausing to ‘think before you click’ can help protect you against such scams.”
Sure has published guidance in response.
It says official emails will use your name, rather than generic “Sir/Madam” or “customer” greetings, and include your customer number.

Pubs can apply to stay open later to show World Cup games
Landowners reminded to clear Guernsey's streams of vegetation
Guernsey homelessness charity 'deeply concerned' at rising support need
Plans lodged to improve Guernsey's sea water Children's Pool
States record £45M surplus, but still warn of Guernsey's funding gap
Warmest Guernsey spring on record
Parent challenges Guernsey school's attendance rule after Prom exclusion
Survey to expose barriers to adult learning in Guernsey