The codes are important for the software companies as they will allow them to suppress Microsoft's own security "pop-ups" if a PC user decides to buy alternative security software, thus keeping brands distinct from that of Microsoft.
Separately, Microsoft has yet to develop promised software essential to the companies so they can block "spyware" and other malicious software.
It will give Symantec , McAfee and other security firms access to the core, or "kernel," of the 64-bit version of Vista, the new Windows operating system due for release in January.
Software firms had access to the kernel in the past until Microsoft redesigned its software to block them.
The codes are part of changes Microsoft said last week it would make after the European Commission, the EU's top antitrust authority, said it had concerns that Microsoft's design of Vista could push some software makers out of the market.
The data in question are Application Program Interfaces, or APIs, which are in essence levers or buttons that other companies call upon so their software will run on Windows.
The APIs are expected to be made available on a Web site to which security software providers have exclusive access, a Brussels-based spokesman for Microsoft said.
Other software makers, such as Adobe , maker of the fixed document format (pdf) software, and Google , the search engine, were also worried about Vista because of the way Microsoft had tied in its own software with similar functions.
On Monday, the Commission said it was up to those companies to judge whether they were happy with the Vista changes.
Microsoft's Ballmer said he believed the announced changes would satisfy the EU executive.