Officials say ransomware known as "WannaCry," has attacked agencies in at least 99 countries.
The attack is believed to be the biggest of its kind ever recorded, disrupting services in nations as diverse as the U.S., Russia, Ukraine, Spain and India. Europol, the European Union's police agency, said the onslaught was at "an unprecedented level and will require a complex international investigation to identify the culprits."
PHOTO: DHS
Ransomware is a type of malicious software that infects a computer and restricts users' access to it until a ransom is paid to unlock it.
Among the worst hit was the National Health Service in England and Scotland.
It was not yet known who perpetrated Friday's attacks. Two security firms -- Kaspersky Lab and Avast -- said they had identified the malicious software behind the attack in over 70 countries, although both said the attack had hit Russia the hardest.
PHOTO: AP
The Russian Interior Ministry, which runs the country's police, confirmed it was among those that fell victim to the ransomware, which typically flashes a message demanding a payment to release the user's own data.
In the U.S., FedEx Corp. reported that its Windows computers were "experiencing interference" from malware, but wouldn't say if it had been hit by ransomware.
Spokeswoman Irina Volk was quoted by the Interfax news agency Saturday as saying the problem had been "localized" and that no information was compromised.
-- What to do next --
U.S. officials are encouraging everyone to update their operating systems to avoid attacks.
They also advise you not to click on or download unfamiliar links or files.
And be sure to back up your data to prevent a possible loss.
DHS said Microsoft released a patch in March that addresses this specific vulnerability, and installing this patch will help secure your systems from the threat.
Microsoft says it will make the fixes free for everyone.
For more information visit the DHS website.
The Associated Press contributed to this report.