Intel, largely by virtue of its success, has the most at stake. While the Pentium chip underpinned most PCs running Microsoft operating systems in 1994, Intel processors are now also used in all Apple Macintosh systems and more than 95 percent of the chips used by cloud services and data centers run by corporations. Its technological reach means that both Meltdown and Spectre could affect just about anyone who uses the internet.

“We created a microprocessor monoculture,” said Bryan Cantrill, chief technology officer at Joyent, a cloud service owned by Samsung. “There are dangers associated with that.”

Intel’s situation is complicated by history and semantics. The Pentium problem was caused by a design error. But Meltdown and Spectre attacks exploit a common speed-boosting technique in chips called speculative execution that Intel’s Mr. Smith insisted is working as it should. That approach to chip design emerged before researchers developed new ways to spy on such internal operations, using what they call “side-channel” analysis, Mr. Smith said.

As a result, the security issues that were discovered were not flaws or bugs, he said. The features that hackers could exploit are a bit like a door or window in a house, which burglars can exploit but that builders would not consider leaving out.

That hasn’t stopped an uproar from security researchers and tech industry executives. One widely distributed barb came from Linus Torvalds, the creator of the Linux operating system, who posted a testy message last week advising Intel to “take a long hard look” at its chips “and actually admit that they have issues instead of writing P.R. blurbs that say that everything works as designed.”

Major users of Intel chips — including Apple and the cloud computing arms of Google and Amazon — have said they deployed security fixes recommended by Intel and so far they have not reported the sharp performance slowdowns of the sort some experts projected.