Yahoo Xtra customers are being warned about a spam email that has been been sent to a number of people.
Telecom retail chief executive Chris Quin said the email claims to be from the Yahoo Security Department and asks customers to download an attached file in order to verify their account.
Mr Quin says the message is not from Yahoo nor from Telecom, and the attachment may be malicious.
Telecom is advising customers who receive any suspicious-looking emails to delete them immediately and never click on any of the links within them or download any attached files. It says this advice applies even if the email appears to be from a known contact.