Telecom New Zealand is urging its users to change their email passwords following a nationwide spam attack.

Hundreds of Kiwis have received numerous spam emails in the last few days due to a suspected phishing issue where emails are hijacked by spammers attempting to gain confidential information and credit card details from users.

Yahoo's Xtra email service was hit by a phishing issue over the weekend.

The issue was first noticed when Yahoo's email servers - Xtra email - sent out hundreds of spam emails to users' contact lists.

Telecom spokeswoman Harriet Muir says the company was informed of a suspected phishing issue at 4pm on Saturday.

'Some customers reported experiencing bounced emails and noticed emails were being sent to their contact list after opening suspicious emails.”

Phishing is a tactic used by scammers to acquire usernames and passwords off unsuspecting internet users. The fraud uses what seems to be a trustworthy website or email address to gather the information.

It isn't known how the Yahoo Xtra email security was breached, but once it was, emails were sent to everyone on the users' contact lists asking them to click on a link.

Yahoo! advised Telecom at 1am on Sunday morning the issue had been resolved, however the company is still asking customers who have received spam emails not to open them or the website link.

Customers will also need to change their password to avoid further issues, says Harriet.

The spam characteristics include emails will be from a recognised email address known to you, it will be either a yahoo or Xtra email address and will contain only a link which you are advised not to open

Users should contact the Broadband Helpdesk on 0800 225 598 about any problems.