A ‘kill switch’ is slowing the spread of WannaCry ransomware

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Friday’s unprecedented ransomware attack may have stopped spreading to new machines — at least briefly — thanks to a “kill switch” that a security researcher has activated.

The ransomware, called Wana Decryptor or WannaCry, has been found infecting machines across the globe. It works by exploiting a Windows vulnerability that the U.S. National Security Agency may have used for spying.

The malware encrypts data on a PC and shows users a note demanding $300 in bitcoin to have their data decrypted. Images of the ransom note have been circulating on Twitter. Security experts have detected tens of thousands of attacks, apparently spreading over LANs and the internet like a computer worm.

However, the ransomware also contains a kill switch that may have backfired on its developers, according to security researchers.

Wana Decryptor infects systems through a malicious program that first tries to connect to an unregistered web domain. The kill switch appears to work like this: If the malicious program can’t connect to the domain, it’ll proceed with the infection. If the connection succeeds, the program will stop the attack.

A security researcher who goes by the name MalwareTech found that he could activate the kill switch by registering the web domain and posting a page on it.

MalwareTech’s original intention was to track the ransomware’s spread through the domain it was contacting. “It came to light that a side effect of us registering the domain stopped the spread of the infection,” he said in an email.

img 20170512 095943Michael Kan

The Wanna Decryptor ransomware’s ransom note. 

Security firm Malwarebytes and Cisco’s Talos security group reported the same findings and said new ransomware infections appear to have slowed since the kill switch was activated.

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