One of the UK’s biggest bus companies has fallen victim to a cyber attack.

Go-Ahead Group announced that it is “managing a cyber security incident” after “unauthorised activity” was detected on its network on Monday.

The company also runs train operator Govia Thameslink Railway in a joint venture with Keolis, but said that was unaffected as it runs on a different system.

A spokesman for Go-Ahead said there was “no indication that any customer data has been compromised”.

There is no impact on UK or international rail services

In a statement, the Newcastle-based company said: “Upon becoming aware of the incident, Go-Ahead immediately engaged external forensic specialists and has taken precautionary measures with its IT infrastructure whilst it continues to investigate the nature and extent of the incident and implement its incident response plans.

“Go-Ahead will continue to assess the potential impact of the incident but confirms that there is no impact on UK or international rail services which are operating normally.”

It added that it has notified the Information Commissioner’s Office (ICO) “as a precaution”.

Go-Ahead is the largest bus operator in London, and also runs services elsewhere in England, particularly in the North East, East Anglia and the South.

British Airways was fined £20 million by the ICO over a 2018 data hack.

Investigators found that the airline should have identified the security weaknesses which enabled the attack to take place, and failed to protect the personal and financial details of more than 400,000 customers.

Italy’s state railway company Ferrovie dello Stato temporarily suspended some ticket sales in March after discovering signs of a cyber attack.