The month-long clean-up - dubbed a "code scrub" by Microsoft - targets everything from desktop operating systems to its newly released .net tools.
The development team building the next version of Windows, for example, has taken a break to perform an "intense review of the Windows source code," said a Microsoft spokeswoman.
Similar efforts are under way with the development team building Microsoft's Office software and among developers working on its .net initiative. The process will extend to other divisions at Microsoft over the next few months.
The cleaning frenzy is part of Microsoft's broader Trustworthy Computing Initiative, which Bill Gates outlined in January.
Although many users will welcome the move, Michael Silver, a software analyst with Gartner, warned that the moratorium on new code could hit Microsoft's development schedule.
Most at risk is the first major package of updates and bug fixes for Windows XP, Microsoft's newest operating system. The service pack is expected to include the updates, patches and bug fixes developed for the operating system since its launch in October.
The service pack already faced a possible delay because of a stipulation in the proposed settlement of Microsoft's long running dispute with the US Department of Justice. The settlement requires Microsoft to disclose certain application program interfaces (APIs) for the operating system within a year of the deal being signed or in the first Windows XP service pack; whichever comes first.
Microsoft typically releases the first service pack some six months after the product is launched. That puts the Windows XP Service Pack 1 due for release around April. It is now unclear whether the company can meet that deadline, Silver said.