YahooXtra customers have been hit with another wave of spam attacks, forcing Telecom to lock down users' email accounts.
It's unknown how many are affected, but an attack in February compromised around 87,000 accounts.
Telecom spokesman Richard Llewellyn said customers would be locked out until they changed their password.
"If Yahoo identifies an account as having been compromised, they will block the account until the customer resets their password.''
Mr Llewellyn said the company became aware Yahoo had been experiencing spam-related issues yesterday morning.
"This in turn affected some Yahoo! Xtra customer accounts in New Zealand.
Any customers who have received mail that they believe is spam, even from a known contact, should delete it immediately and should not click on any suspicious links contained within emails,'' he said.
Telecom continually monitored its email service for these types of issues. Blocking email accounts identified by Yahoo as compromised until the customer reset the password and re-secured their account was standard practice, Mr Llewellyn said.
"That process has been implemented for accounts affected by this incident.''
The fastest way for affected customers to do this was online, he said.
Customers whose accounts have been blocked and who want guidance on how to reset and re-secure their passwords can find it here.
- Additional reporting Newstalk ZB