After a massive cyber-attack on Friday night, some security experts have warned that another make take place on Monday. British security researcher Malware Tech told the BBC that there is “another one coming... quite likely on Monday”. Friday’s hacking had affected more than 125,000 systems in over 150 countries.

Cybersecurity experts told Reuters that a new version of the malware, which has been dubbed “WannaCry”, are expected soon. The bug had only affected Windows systems, as the malware used a Microsoft update to “spread across networks”.

Rob Wainwright, Director of Europol, the European Union’s police agency, said at least 200,000 victims were affected. “The global reach is unprecedented. The latest count is over 200,000 victims in at least 150 countries, and those victims, many of those will be businesses, including large corporations,” he said.

The cyber attack is believed to have been developed by using a leaked code from the United States National Security Agency. Researchers from various cyber security firms said the hackers, who have not yet identified themselves, made a self-spreading malware by exploiting a piece of NSA code. The code, known as “Eternal Blue”, was stolen and released on April 14 by a group called Shadow Brokers.

The US Department of Homeland Security said that it was ready to lend technical support to contain the spread of the malware. Meanwhile, whistleblower Edward Snowden blamed the NSA for the breach, according to The Guardian. “If NSAGov had privately disclosed the flaw used to attack hospitals when they *found* it, not when they lost it, this may not have happened,” he tweeted.

The first casualty of these global cyber attacks was the National Health Service in UK. The cyber attack led to chaos in some places, with appointments being cancelled, patients turned away and phone lines disrupted. Besides the NHS, some Spanish companies were soon affected by the attack too. Telecom company Telefonica was one such firm. Later, reports poured in from Portugal, Russia, Ukraine and Taiwan. In US, the affect was the least, according to Reuters. However, the attack did manage to hit systems at US shipping firm FedEx.