Gumtree, a subsidiary of eBay, notified affected customers of the security breach on Friday.

"We are writing to let you know that some of your Gumtree account information was compromised in a security attack last weekend," the company wrote in an email.

"The attackers accessed your email address. Contact names and phone numbers, which are made publicly available on the site if provided, were also accessed."

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."

Gumtree advised affected users to be wary of fake emails and phishing scams, which use personal information to trick victims into handing over further sensitive information such as credit card or banking details.

The company also recommends choosing strong passwords and not using the same login combinatons for different services.

It's not clear how many customers were affected by the breach.