The 'doomsday virus', as it's being called, already has been uploaded hundreds of thousands of times. The FBI discovered the malware officially known as DNS Changer last November.
The agency dismantled a ring of Estonian hackers whose malicious software infected machines without users knowing it.
It's designed to divert users to fake and dangerous sites so hackers can steal their information.
The FBI took DNS changer down and had been running a backup system to keep people online.
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It's had been running for eight months but this afternoon at 2 pm Australian Eastern Standard time they will pull the plug on it.
If you are worried that your computer has been infected you can run a quick check by clicking here.
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