Microsoft's programmers have been ordered to drop everything and work on fixing security problems.
Bill Gates has reportedly emailed 7,000 workers ordering them to concentrate solely on finding bugs in Windows 2000 and Windows XP.
The move follows a series of security flaws, including one on Internet Explorer that could have allowed hackers remote access to users' computers.
The urgent code review includes a two-day training seminar for all programmers called "writing secured code".
The session will be aimed at making sure embarrassing bugs do not show up in the future.
Reports claim that in his memo to workers, Mr Gates said: "All those great features won't matter unless customers trust our software.
"So now, when we face a choice between adding features and resolving security issues, we need to choose security."
Computer industry analyst Michael Silver said companies and users now want to know they are not vulnerable to hackers.
"Companies don't want new features, they want products that work and are secure," he said.