Spark says its Yahoo! Xtra email service was probably not hacked again despite spam apparently being sent from customer accounts.
The telecommunications giant has been under fire again since last night after reports of suspicious emails from Xtra addresses.
This follows a hacking attack in February when more than 60,000 accounts were compromised.
Spark communications manager Lucy Fullarton said the suspicious activity was most likely ''email spoofing'' where cyber criminals forge the sender's email address.
The incident was still being investigated but indications were that customers' accounts had not been hacked. Spark did not know how many customers were affected.
She said if it was spoofing there was no guarantee it would not happen again.
''The difficulty with spoofing is because it's not going through the Yahoo servers or through our systems there's little we can do about it.''
Ms Fullarton defended Spark's record with email security and said the company had kept customers updated with advice.
''We're always looking at what we can do better but these criminals are extremely sophisticated and they're constantly changing their methods, so we have to constantly keep up.''
She said any suspicious emails should be deleted and the links in them should not be clicked on.
Email users should also choose a sophisticated password and never go back to a password used in the past.
