A flaw in Intel microprocessors is leaving computers worldwide facing up to a 50% slowdown when performing particular tasks.
The flaw affects a mechanism that microprocessers use to perform tasks quickly.
It is the fix that will cause the slowdown, as developers try to prevent hackers taking advantage of the flaw.
"Some things will end up being twice as slow as they are today," Mr Ian Pratt, formerly a senior lecturer at the University of Cambridge, told Sky News - but not every process would be affected.
"You won't really notice it with web browsing and editing documents. It's an interesting one with gaming, because gaming is very graphics intensive, but most graphics these days don't involve systems calls.
"The overheard will be most noticeable on graphics games, but it's going to be quite low there."
People who work with graphing applications or large spreadsheets on their home computers will experience this processing slowdown, said Mr Pratt, but those browsing the web or mining Bitcoin would not.
Computer users are being urged to still apply updates to their computers, despite the potential slowdown.
A spokesperson for the National Cyber Security Centre told Sky News: "We are aware of reports about a potential flaw affecting some computer processors.
"At this stage there is no evidence of any malicious exploitation and patches are being produced for the major platforms.
"NCSC advises that all organisations and home users continue to protect their systems from threats by installing patches, as soon as they become available."
:: Technical Issue
Details of the flaw and how it might be exploited are being kept strictly under wraps while programmers rush to redesign operating systems including Windows and Linux to work around the bug.
The issue affects a process that computer chips use to work faster. The redesigns will leave computers performing much slower than they could if they were left vulnerable to attack.
Mr Pratt explained: "For about 20 years, all central processing units (CPUs) have used a technique called 'speculative execution' which is a way of getting better performance from the processor.
"You write your program, which is a list of statements that get turned into machine code for things for the CPU to do.
"Modern CPUs can look hundreds of instructions ahead in the program code for work to do, but some of these instructions - if they are a branch of the code - may never get executed.
"Work that the CPU does speculatively, before it is executed, stays hidden in a special layer between the CPU and the operating system called the kernel."
Researchers fear that the hardware flaw means that this work may not necessarily remain hidden and speculate that an attacker might be able to steal passwords or other key information from the computer.
"I wouldn't throw Intel under the bus on this," Mr Pratt added. "This is a class of attack called a 'sidechannel attack' which will affect many vendors.
"Operating system vendors are making fairly significant changes to work around this issue. This is going to be one of the most complex security updates any OS vendor has ever had to deliver."
He did not believe that any attack would necessarily allow an attacker to read a secret key directly from the kernel - but it could allow them to learn details about the kernel to support additional attacks.
"Primarily it's a problem for servers," said Mr Pratt.
Companies which offer large cloud-computing products such as Amazon, Google, and Microsoft may be heavily affected.
Amazon and Google were not immediately able to offer comment.
Microsoft and Apple told Sky News they had no comment to offer.
Intel said in a statement that the flaw was not unique to Intel products and said it does not have the potential to "corrupt, modify or delete data".
It added: "Contrary to some reports, any performance impacts are workload-dependent, and, for the average computer user, should not be significant and will be mitigated over time.
"Check with your operating system vendor or system manufacturer and apply any available updates as soon as they are available. Following good security practices that protect against malware in general will also help protect against possible exploitation until updates can be applied."
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