Experts on cyberwar are worried that there is a global cyber-attack underway after a series of very serious incidents in Ukraine, Russia, Denmark.

According to the Independent, Ukraine has suffered the hardest cyber-attack in its history.

The attack is hitting major infrastructure in the countries where it has spread to. That has included companies ranging as widely as Danish shipping company Maersk and British advertising company WPP.

Some security experts have even suggested the attack could be bigger than the Wannacry attack, which spread across the world in May.

According to cyber security experts, they don’t yet know whether it’s possible to mitigate against the attack, or how it gets into computers.

Russia’s top oil producer Rosneft said a large-scale cyber attack hit its servers on Tuesday and computer systems at some banks.