Westpac Australia is warning customers to delete a spam email with the subject line `Westpac Secure Email Notification' which claims that they have received a secure message.

The claims that the customer can only read the message if they open an attachment first.

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"You will be prompted to open (view) the file or save (download) it to your computer. For best results, save the file first, then open it with Internet Explorer," read the email.

To ally people's suspicions, the email includes a phone number, (866) 535 7706, for a secure email help desk.

A Westpac spokesperson said that it would never ask customers to update, verify or correct any online banking details directly into an email reply.

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"If you have responded to this email and believe your security has been compromised, or notice a transaction you did not make, contact us immediately on 132 032," the spokesperson said. "Do not use online banking until you have up-to-date security software on your computer."

On September 11, National Australia Bank (NAB) issued a warning to customers to delete an SMS message that claimed unusual activity had been detected on their bank account.

The SMS re-directs customers to click a link that sends them to a fake NAB website where they are then asked to enter their credit card and personal details.

"If you have received an SMS message of this type and have responded, please contact your local NAB branch or call 13 22 65 immediately," said a NAB spokesperson at the time.

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