GENEVA — A Swiss mobile phone operator says its data systems were breached late last year and the contact details of about 800,000 customers were compromised.

Swisscom said Wednesday that the names, addresses, telephone numbers and date of birth of the customers was accessed by an unknown party, which got the data through a sales partner of Swisscom.

It said that passwords, conversations and payment data were not affected and that it has not received any reports of customers suffering as a result.

Swisscom said it discovered the incident through a routine check of its activities and is carrying out an in-depth investigation.

The 800,000 customers represent almost 10 percent of Switzerland’s overall population.