Zoopla this evening said that its software system Alto was subject to ‘unauthorised entry’. It has now moved to reassure agents that no data was stolen.

The attempted hack on Alto happened on Friday night but, says Zoopla, was quickly detected by its cyber security systems, “within an hour”, resulting in Alto being down for some five to six hours.

Zoopla told EYE that it does not know who was behind the hack, or why.

However it emphasised that no customer details were viewed or downloaded.

Zoopla is emailing all its Alto agents tonight about the incident.

It says it is taking steps to ensure it does not happen again, in particular re-setting log-ins.

However Zoopla does say that it is up to Alto customers to notify the attack to EU data protection authorities or to their clients.

Zoopla says: “We do not believe that this is required because there is no risk to their clients resulting from their personal data being temporarily unavailable.”