WASHINGTON D.C. (REUTERS) - Cyber security experts are warning that new versions of the ransomware that crippled businesses and schools across the globe may wreak fresh havoc on Monday (May 15) when employees return to work.

US and European officials are scrambling to catch the culprits behind the virus - dubbed "WannaCry" - that first struck on Friday and stretched across some 200,000 businesses in more than 150 countries, forcing victims to pay hundreds of dollars each to regain access to their computers.

US President Donald Trump has ordered homeland security advisor Tom Bossert to convene an "emergency meeting" to assess the threat in its aftermath, with top US security officials holding a second meeting on Saturday to help mitigate the damage.

The original attack lost some momentum late on Friday after a security researcher in Britain, who uses the Twitter handle @MalwareTechBlog, stumbled on a way to temporarily limit the worm's spread. But cyber experts - including the head of the European Union police agency - warn the respite could be short-lived.

Affected businesses include FedEx, Nissan, German rail operator Deutsche Bahn and hundreds of hospitals and clinics in the British National Health Service.