Major firms, airports and government departments in Ukraine have been hit by a massive cyber attack which has spread across Europe on Tuesday.
Ukrainian banks, companies, the capital Kiev's largest airport and government network have been affected.
Ukrainian Prime Minister Volodymyr Groysman said a wave of cyber attacks on Ukrainian state institutions and companies on Tuesday was "unprecedented" but had not hit "important" IT systems.
The secretary of the country's Security Council said there were signs of Russian involvement in the cyber attacks.
The Interior Ministry said the attacks are using a modified version of the "Wannacry" virus, adding that it is the biggest in Ukraine's history.
Kiev's main airport was also affected by a "spam attack," so some flights will be delayed.
Rosneft's announcement. /Reuters Photo
Russian oil giants Rosneft announced on Tuesday that its websites were shut down following the large-scale cyber attack on its servers, but production has not been affected due to a timely switch to a backup system.
The world's biggest advertising company, WPP, said that several of its agencies had been affected.
"IT systems in several WPP companies have been affected by a suspected cyber attack," the company said in a statement, adding that they are assessing the situation and appropriate measures will be taken.
Dutch company APM Terminals, subsidiary of shipping giant Maersk has suffered from a cyber attack. /AP Photo
Dutch company APM Terminals, subsidiary of shipping giant Maersk, has also suffered, with its 17 shipping container terminals hacked, two in Rotterdam and 15 in other parts of the world, according to Dutch broadcaster RTV Rijnmond.
The company's website as well as the phones at its headquarters in The Hague was difficult to reach.
(With inputs from Reuters)