Hackers are using New Zealanders' email accounts to send out thousands of spam messages, and Telecom admits it still doesn't know the cause or scale of the problem.
Computer users with Yahoo! Xtra email accounts are being advised to immediately delete any suspicious emails they receive, even if they apparently come from known contacts.
On Friday, Telecom said it was working with Yahoo! to investigate the issue, and suspicious emails, often with "Hi" or "Hello" in the subject line, have flooded email inboxes since.
Yesterday a Telecom spokeswoman said that the company was urgently seeking answers to the issue.
"At this point we don't have confirmation of the cause or the scale of the problem.