Croydon Council's website was recently hacked in an attempt to mine cryptocurrency using visitors' computers.

Security researcher Scott Helme said more than 4000 websites were hacked as part of the operation, which took place over the weekend.

"A third party provider was compromised and their JS library was altered," Mr Helme posted on his website.

"The alteration introduced a crypto mining script that was then subsequently included on over 4,000 websites that I know of, many of which were Government websites."

He said visitors were no longer at risk of visiting the affected websites.

A spokesman for Croydon Council put out a statement assuring people that no information had been stolen as a result of the security breach.

"We would like to reassure our website users that no council data or information has been accessed or compromised during this worldwide cyberattack," he said.

"As a precaution we are working closely with our web partners to review the security of any third party software and accessibility services that we use to mitigate against any future threat."