Russia's Rosneft, one of the world's biggest crude producers by volume, said its systems had suffered "serious consequences", but added oil production had not been affected because it switched over to backup systems.
There's very little information about who might be behind the disruption at each specific company, but cybersecurity experts rapidly zeroed in on a form of ransomware, the name given to programs that hold data hostage by scrambling it until a payment is made. Yet an analyst from Kaspersky Lab told NPR that the outbreak is coming from a "new ransomware we haven't seen before".
Russian Federation and Ukraine were most affected by the thousands of attacks, according to security software maker Kaspersky Lab, with other victims spread across countries including Britain, France, Germany, Italy, Poland and the United States.
Researchers told ABC News that they do not believe that a nation state was behind the attack and suggested that it could have been launched by a lone cybercriminal. This likely has a lot to do with how much was priced in last month following the WannaCry ransomware breakout, as well as how easy it is to secure systems against the particular exploit that both attacks rely on.
The cyberattack came as global cybersecurity leaders have convened in Tel Aviv this week to discuss the future of cybersecurity threats at an worldwide conference.
A large-scale cyberattack is working its way through a number of Ukrainian and Russian targets today (June 27).
After the Wannacry attack, organisations around the globe were advised to beef up IT security.
DLA Piper is dealing with a ransomware attack on Tuesday that is apparently affecting offices in the United States, Europe and the Middle East. "We can confirm the breakdown is caused by a cyber attack", a spokeswoman said.
In Ukraine, the power grid, banks and government offices were hit, leading the country's prime minister to call the breach, "unprecedented". Indian subsidiaries of United Kingdom and Russia-based oil and gas, energy and aviation companies were also hit.
The companies affected were hit by a type of ransomware that locks users out of the computer and demands purchase of a key to reinstate access, Group IB said.
A Ukrainian media company said its computers were blocked and it was asked to pay $300 in the crypto-currency bitcoin to regain access.
"We are talking about a cyberattack", said Anders Rosendahl, a spokesman for the Copenhagen-based group.
Ukrainian Deputy Prime Minister Pavlo Rozenko said the government's computer network went down and the central bank reported disruption to operations at banks and firms including the state power distributor. "If an attack gets through your defenses you must have data threat detection techniques applied to your data environment to indicate anomalies to standard operation and highlight proper recover points to escape the ransomware threat".
Netherlands-based shipping company TNT said some of its systems needed "remediation".
The US Department of Homeland Security said it was monitoring the attacks and coordinating with other countries.
The fight against cyberattacks has sparked exponential growth in global protection spending, with the cyber security market estimated at $120 billion this year, more than 30 times its size just over a decade ago.