MOSCOW, June 27. /TASS/. Russian top oil producer Rosneft has reported "a powerful hacker attack" on its servers on Tuesday.

"A powerful hacker attack has been carried out on the company's servers, and we hope that this has nothing to do with the current judicial procedures. The company has appealed to the law enforcement agencies on the fact of cyber attacks," Rosneft said in a statement.

An official with the company also told TASS that after the attack Rosneft switched over to a reserve management system.

"The hacker attack could have led to serious consequences, but thanks to switching to the reserve management system neither oil production nor oil treatment have been halted," the official said.

Also Rosneft’s press secretary Mikhail Leontyev told TASS that after the attack the oil company and its subsidiaries are operating as usual.

"Rosneft and its subsidiaries are operating on a regular basis. Those who spread fake and panic messages will be brought to responsibility together with those who are behind the hacker attack, "Leontyev said.

At present, the websites of Rosneft and Bashneft are not operating.

Earlier the Vedomosti newspaper wrote referring to a source that all the computers at the refinery of Bashneft, Bashneft-Produkt and the Bashneft management rebooted simultaneously and after that uninstalled software was downloaded and the screensaver of the WannaCry virus was displayed on the screen.

On Tuesday, the Arbitration Court of the republic of Bashkortostan considered the lawsuit filed by Rosneft and Bashneft against Sistema Holding and its subsidiary Sistema-Invest on the recovery of 170.6 billion rubles ($2.9 bln) of losses suffered by Bashneft in the result of the reorganization in 2014.