TPG Telecom has been hit by a security breach that may impact up to 15,000 iiNet and Westnet customers.

Cyber security firm Mandiant discovered unauthorised access to the server that hosts up to 15,000 iiNet and Westnet business customer e-mail accounts.

“It appears the primary aim of the threat actor was to search for customers’ cryptocurrency and financial information,” TPG said.

Personal accounts were not affected. “We continue to investigate the incident and any potential impact on customers and are advising customers to take necessary precautions.

“We have implemented measures to stop the unauthorised access, further security measures have been put in place, and we are in the process of contacting all affected customers on the hosted exchange service. We have notified the relevant government authorities.”

Shares in TPG have fallen close to 5 per cent this morning.