Windows 7, not XP, was the reason last week’s WCry worm spread so widely

Enlarge (credit: Kaspersky Lab)

Eight days ago, the WCry ransomware worm attacked more than 200,000 computers in 150 countries. The outbreak prompted infected hospitals to turn away patients and shut down computers in banks and telecoms. Now that researchers have had time to analyze the self-replicating attack, they're learning details that shed new and sometimes surprising light on the world's biggest ransomware attack.

Chief among the revelations: more than 97 percent of infections hit computers running Windows 7, according to attacks seen by antivirus provider Kaspersky Lab. By contrast, infected Windows XP machines were practically non-existent, and those XP PCs that were compromised were likely manually infected by their owners for testing purposes. That's according to Costin Raiu, director of Kaspersky Lab's Global Research and Analysis Team, who spoke to Ars.

While the estimates are based only on computers that run Kaspersky software, as opposed to all computers on the Internet, there's little question Windows 7 was overwhelmingly affected by WCry, which is also known as "WannaCry" and "WannaCrypt." Security ratings firm BitSight found that 67 percent of infections hit Windows 7, Reuters reported.

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