Hundreds of ticket machines operated by Northern have been put out of action by a cyber attack.
The company said it appeared to be a ransomware attack, but that no customer or payment data had been compromised.
Northern's self-service ticket machines have been offline since last week and an investigation has been launched.
The government-run company said it had taken 'swift action' and that only the servers which operate the ticket machines had been affected.
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In a statement Northern said: "This is the subject of an ongoing investigation with our supplier, but indications are that the ticket machine service has been subject to a ransomware cyber-attack."
It come just two months after Northern installed 621 touch screen machines at 420 stations at a cost of £17m.
Customers can still buy tickets through the app or website, and they can be collected from ticket offices.
Northern apologised for 'any inconvenience' caused.
The company added: "We are working to restore normal operation to our ticket machines as soon as possible.
"Customers who have already bought tickets to be collected at a machine, or who would normally use 'promise to pay' slips, should board their booked service and either speak to the conductor or to Northern staff at their destination station."
The Northern rail franchise, which runs trains between towns and cities across northern England including Manchester, Leeds and Sheffield, was nationalised in 2020 after years of delays, cancellations and strikes.
