Eurostar has reset its customers’ login passwords after detecting attempts to break into an unspecified number of accounts.
The rail service said it had notified those whose accounts had been targeted.
Other passengers will be told they have been blocked the next time they try to log in and will be asked to reset their details.
The firm declined to say whether any of the hack attacks were successful but said payment details were not affected.
“We believe this to be an unauthorised automated attempt to access customer accounts,” a spokesman said in a statement.