"The company is taking this matter extremely seriously and has initiated a thorough investigation into the cause, content and implications of the leak," Yandex's Dutch holding company said in a statement.

It said it found no evidence that users' personal information had been impacted but that the code contained the contact details of some of its partners.

"Many of these and other issues which came to light following the code leak have already been fixed or are in the process of being fixed," it said.

Since Russia sent its armed forces into Ukraine last February, websites of many Russian companies and news websites have suffered sporadic hacking attempts.

A data leak in March exposed the personal details of more than 58,000 people on Yandex's food delivery app, Yandex.Eda.

(Reporting by Reuters; Writing by Caleb Davis; Editing by Christina Fincher)