A security researcher has told the BBC how he “accidentally” halted the spread of ransomware affecting hundreds of organisations, including the UK’s NHS.
The man, known online as MalwareTech, was analysing the code behind the malware on Friday night when he made his discovery.
He first noticed that the malware was trying to contact an unusual web address – iuqerfsodp9ifjaposdfjhgosurijfaewrwergwea.com – but this address was not connected to a website, because nobody had registered it.
So, every time the malware tried to contact the mysterious website, it failed – and then set about doing its damage.
MalwareTech decided to spend £8.50 and claim the web address. By owning the web address, he could also access analytical data and get an idea of how widespread the ransomware was.
But he later realised that registering the web address had also stopped the malware trying to spread itself.
“It was actually partly accidental,” he told the BBC.
Originally it was suggested that whoever created the malware had included a “kill switch” – a way of stopping it from spreading, perhaps if things got out of hand.
But MalwareTech now thinks the coder had included a mechanism to stop security researchers analysing the malware, which backfired.
Security researchers often analyse viruses on a virtual machine or “sandbox” – a secured, disposable computer environment with no important files that might be destroyed.
MalwareTech now thinks the software’s attempt to contact the mysterious web address – iuqerfsodp9ifjaposdfjhgosurijfaewrwergwea.com – was a way of checking whether the malware was being analysed on a sandbox.
On a real computer, the website would fail to load. But a virtual machine might behave differently.
“The malware exits to prevent further analysis,” MalwareTech wrote in a blog post.
“My registration… caused all infections globally to believe they were inside a sandbox and exit… thus we initially unintentionally prevented the spread and further ransoming of computers.”
Does this mean the ransomware is defeated?
While the registration of the web address appears to have stopped one strain of the malware spreading, it does not mean the ransomware itself has been defeated.
Any files that were scrambled by the ransomware will still be held to ransom.
Security experts have also warned that new variants of the malware that ignore the “kill switch” will appear.
“This variant shouldn’t be spreading any further, however there’ll almost certainly be copycats,” said security researcher Troy Hunt in a blog post.