Tasnim � The Iranian Cyber Police issued a security alert to all Internet users in the country, encouraging people and organizations to update their operating systems to ward off a massive wave of cyberattacks across the globe that seize control of computers until the victims pay a ransom.

In a warning on Saturday, Lieutenant Colonel Ali Niknafas, a commander of the Cyber Police -known as FATA in Iran- called on all users to update their computer and network systems to avoid being affected by the ransomware, called "WannaCry� or "WannaCrypt."

Hospitals, major companies and government offices in 99 countries have been hit by the ransomware.

Cybersecurity firm Avast said it had identified more than 75,000 ransomware attacks in the world, making it one of the broadest and most damaging cyberattacks in history.

Avast said the majority of the attacks targeted Russia, Ukraine and Taiwan. But British hospitals, Chinese universities and global firms also reported they had come under assault.

WannaCry locks down all the files on an infected computer and asks the computer's administrator to pay in order to regain control of them. The ransomware is spread by taking advantage of a Windows vulnerability that Microsoft released a security patch for in March.

In the wake of the attack, Microsoft said it had taken the "highly unusual step" of releasing a patch for computers running older operating systems including Windows XP, Windows 8 and Windows Server 2003.