The UK's National Crime Agency (NCA) two-week timeframe to protect computers from the threats posed by the GoZeus and Cryptolocker scams is set to expire in just a few hours, with crooks set to have the systems back up and running.
The NCA issued its advice about the Trojan software earlier in June saying that users had a two-week window in which the network would not be active, and during which they would be able to rid themselves of infection.
The NCA confirmed on Monday that while many have heeded this advice, thousands of machines remain at risk.
"Current indications are that UK GoZeuS and CryptoLocker infections have reduced since 2 June, but thousands of systems remain affected or at risk," it said.
"By updating security software, running system scans to detect and clear infections, and checking that computer operating systems are up to date, individuals and businesses can take advantage of the criminal network's relative weakness."
The NCA warned that by midnight on Tuesday, 17 June, the two week window would have passed, although it is not clear exactly why the NCA has been so rigid with this timeframe.
Andy Archibald, deputy director of the NCA's National Cyber Crime Unit, said that while security is always important the few remaining days left before it expects the threats to come back online should be used as soon as possible.
"This is about taking a few simple steps to keep your money and personal information in your hands, rather than those of international criminals," he said.
"While there is never a bad time to maximise your online security, and it is something we should all do regularly, acting now can provide unprecedented levels of protection from these types of malware. If you haven't already, we urge individuals and small businesses alike to take action."
Intel wants to get inside your car, despite missing out on mobile
'We'll keep fighting to fight to keep the web free and open,' claim EFF
Breached in March by the same attackers, claim 'insiders'
And all for less than £150, according to Keith