A serious flaw in the design of Intel's chips will require Microsoft, Linux and Apple to update operating systems for computers around the world.
Intel has not yet released the details of the vulnerability, but it is believed to affect chips in millions of computers from the last decade.
The UK's National Cyber Security Centre (NCSC) said it was aware of the issue and that patches were being produced.
Some experts said a software fix could slow down computers.
"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," the NCSC said in a statement.
"The NCSC advises that all organisations and home users continue to protect their systems from threats by installing patches as soon as they become available."
The bug could allow malicious programs to read the contents of the so-called kernel memory of computers, which can include passwords and login keys.
It is also likely to affect major cloud computing platforms such as Amazon, Microsoft Azure and Google, according to The Register, which broke news of the flaw.
The effects of the updates to Linux and Windows could incur a performance slowdown of between five and 30 percent, experts said. It would involve separating the so-called kernel memory from other processes.
Shares in Intel were down almost 6% in US trading after the issue was revealed.
Experts advised caution on the issue.
"It is significant but whether it will be exploited widely is another matter," said Prof Alan Woodward, from the University of Surrey.
"The actual flaw is being rather tightly kept under wraps but from what researchers have gleaned themselves, it's all to do with a flaw in the way certain Intel CPUs address certain types of memory.
"If it is really bad then it may allow an exploit to read parts of the computer memory that should never be reached."
Intel did not respond to requests for comment.
Semi-conductor chips are found in many of the world's computers. Rival AMD told The Register that its chips were not affected.