Companies and governments are being targeted by an updated version of a known virus, Europol said.

Its warning came as an international cyber attack caused disruption for major organisations including advertising firm WPP, European bank BNP Paribas and parts of the Ukrainian government's computer systems.

Europol, which helps EU member states fight international crime, said the latest attack, the second in as many months, is more sophisticated than one in May that affected the NHS among others. The group is monitoring the spread of the virus.

Europol executive director Rob Wainwright said: "This is another serious ransomware attack with global impact, although the number of victims is not yet known.

"There are clear similarities with the WannaCry attack, but also indications of a more sophisticated attack capability, intended to exploit a range of vulnerabilities.

"It is a demonstration of how cybercrime evolves."