Companies across the globe are reporting that they have been struck by a major ransomware cyber-attack.
British advertising agency WPP is among those to say its IT systems have been disrupted as a consequence.
The virus, the source of which is not yet known, freezes the user’s computer until a ransom in untraceable Bitcoin is paid.
Ukrainian firms, including the state power company and Kiev’s main airport, were among the first to report issues.
The Chernobyl nuclear power plant has also had to monitor radiation levels manually after its Windows-based sensors were shut down.
The Russian anti-virus firm Kaspersky Lab said its analysis showed that there had been about 2,000 attacks – most in Ukraine, Russia and Poland.
The international police organisation Interpol has said it was “closely monitoring” the situation and liaising with its member countries.
Experts suggest the malware is taking advantage of the same weaknesses used by the Wannacry attack last month.
“It initially appeared to be a variant of a piece of ransomware that emerged last year,” said computer scientist Prof Alan Woodward.