NEW YORK: The cyberextortion attack hitting dozens of countries spread quickly and widely thanks to an unusual confluence of factors: a known and highly dangerous security hole in Microsoft Windows, tardy users who didn't apply Microsoft's March software fix, and a software design that allowed the malware to spread quickly once inside university, business and government networks.

Other criminals may be tempted to mimic the success of Friday's "ransomware" attack, which locks up computers and hold people's files for ransom.

THE WORM TURNS ... AND TURNS One of the first "attacks" on the internet came in 1988, when a graduate student named Robert Morris Jr. released a self-replicating and self-propagating program known as a "worm" onto the then-nascent internet.

The Morris worm wasn't malicious, but other nastier variants followed – at first for annoyance, later for criminal purposes, such as stealing passwords. But these worm attacks became harder to pull off as computer owners and software makers shored up their defenses.

Once installed, the malware just locks up that computer without spreading to other machines.

FIGHTING BACK The attack is likely to prompt more organizations to apply the security fixes that would prevent the malware from spreading automatically.

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