"As cybercriminals become more sophisticated, there is simply no way for customers to protect themselves against threats unless they update their systems", Mr Smith said.
More than 75,000 similar attacks reportedly happened in nearly 100 countries, with Russia, Ukraine and Taiwan hardest hit, according to the cybersecurity firm Avast. New versions of the worm are expected, the experts said, and the extent - and economic cost - of the damage from Friday's attack were unclear.
Fortunately, a 22-year-old British researcher and 20-something American security engineer discovered a "kill switch" and unregistered domain that halted the attack, reports the Associated Press.
"If you have a scheduled appointment you are advised to attend as normal unless you are told otherwise". Companies across the company are expected to be running checks and updating software today.
Europol executive director Rob Wainwright had warned on Sunday the situation could worsen when workers return to their offices on Monday after the weekend and logged on.
"It seems inconceivable that organisations such as the NHS are prepared to jeopardise highly confidential patient data or critical infrastructure through inadequate cyber security that relies heavily on out-dated anti-virus technologies, when effective alternatives like file-regeneration are available".
Frenchmen claim cure for WannaCry-infected computers
On Thursday, French computer-security researcher Adrien Guinet found a way to unscramble the files without paying the $300 ransom. Cyber-attacks on the scale of WannaCry may remind organisations about the need to maintain their IT security.
Adams: Wenger couldn't coach his way out of a paper bag
We wait to see if Arsene Wenger and Wayne Rooney are saying goodbye to the league, even if they still have cup finals to come. Arsenal manager Arsene Wenger on his side's prospects of a top-four finish: "I am not a betting man".