Usually users on Gumtree can see the names and phone numbers of sellers, but only if they themselves are signed in. The email addresses would have been a target for hackers however, as combining them with other personal information makes them valuable for phishing and fraud.

Users' Gumtree account passwords remained safe, the company said.

Gumtree does not host its users financial details because sellers and buyers arrange payment directly.

"We resolved the isolated attack within minutes of discovering it and since then we've taken extra steps to protect your information," the email said.

"The safety of our community remains our number one priority and we apologise that you've been affected by this."