A pair of security flaws, named Meltdown and Spectre, could let hackers steal sensitive information from most computers, phones and laptops without the owner realising.
The flaws in processing chips have been identified by computer security researchers leading to a scramble to find fixes.
However, the patches designed to fix computers are likely to make the devices work much slower.
Need A Nerd? computer store manager Adam Soar said the security flaws had wide implications.
“I can basically say that anyone who has a processor [made] since 1995 could be affected,” he said.
“It can leak sensitive information from the kernel, the heart of the system.
“It is incredibly complex. You cannot predict all the side effects of it.”
Mr Soar said there had not been any reports of people being hit by the problem – but that might be because users cannot detect it.
“We haven’t had anybody come in for it,” he said.
Threat Intelligence director Ty Miller told the Sydney Morning Herald patched machines would be less efficient.
“You may lose anywhere between 15 to 30 per cent of your [computer’s] power,” he said.
“Things like starting software, or browsing the internet, may actually slow right down.”
Mr Miller said the issue might have wider implications for anyone using a cloud service.
He said a hacker could tap into the processor of the machine hosting their virtual space and access information from all users of the space.
“With cloud environments one of the core security controls is an attacker can’t access the underlying machine that hosts his service,” he said.
“This vulnerability exposes that and introduces a massive risk to operators in the cloud.
“If you do business in the cloud, you need to make sure your provider is applying the patches and getting their machines up to date.”
The Meltdown flaw is specific to Intel processors.
However the Spectre flaw affects chips from a range of makers.
A statement from Intel said industry testing had revealed there was little impact on users.
“Apple, Amazon, Google and Microsoft are among those reporting that they are seeing little to no performance impact,” it said.