Xtra customers could find themselves locked out of their email accounts today, after a burst of spam issues.
Telecom had seen a rise in the number of YahooXtra email accounts hacked and used to send out malicious spam emails. An alert on the issue was released by the company today.
It was not yet known how many customers might be affected, but it was only a small minority of account holders, spokesman Richard Llewellyn said.
User accounts flagged as compromised had been blocked, requiring customers to change their passwords before being able to re-access their email services.
Xtra customers had faced a year of frequent email hijacking. In February, a hacking attack on Yahoo compromised about 87,000 Xtra accounts.
Spammers then sent out hundreds of thousands of emails to anyone in the customers' contacts lists, forcing Telecom to lock-down tens of thousands of user email accounts. There was no evidence the latest spam issues were related to this hacking, Llewellyn said.
Emails often consisted of a generic greeting and a link to a website asking for personal details including credit card numbers. Users were advised never to click on links from suspicious emails, even from known contacts, and to run anti-virus software if they had.