Computer systems from Russia to Britain were victims of an international cyberattack on Tuesday in a hack that bore similarities to a recent one that crippled tens of thousands of machines worldwide.

As reports of the attack spread quickly, the Ukrainian government said that several of its ministries, local banks and metro systems had been affected. A number of companies — including Rosneft, the Russian energy giant; Saint-Gobain, the French construction materials company; and WPP, the British advertising agency — also said they had been targeted.

It remains unclear who is behind this most recent cyberattack. Like the previous WannaCry attacks in May, Tuesday’s hack takes over computers and demands digital ransom to regain control.

Computer experts were calling the computer virus “Petya,” and said that it was similar to the WannaCry attack that spread like wildfire across much of Asia and Europe.

Analysts have been warning that hackers are increasingly likely to use such ransomware attacks to gain access to people’s computers, both in a bid to cause major global disruption and for financial gain.

That was the case in the recent WannaCry attack, which saw hospitals in the United Kingdom, automakers’ production facilities and German train stations all affected by the computer virus.

The recent attacks appear to evade popular antivirus software. In a test of 61 antivirus solutions, only four successfully identified the ransomware.

Kaspersky, the Russian antivirus firm, first identified the ransomware in March and encountered a sample of the ransomware on June 18, suggests it has been hitting businesses for over a week.