A spokesman for the company told news agency Reuters that Microsoft will launch the free product, code-named Morro, "soon" but did not provide further details.
Microsoft has said previously that Morro will be suitable for use on low-cost, low-powered netbooks that are growing in popularity in emerging markets and in some segments of the North American computer market. Microsoft also is planning to launch versions of Windows 7 that are netbook-compatible.
The definition of malware covers a range of computer threats, including viruses, spyware, rootkits, and Trojans. Hackers, many of them connected to organized crime, often use such tools to extract sensitive data like bank account numbers and passwords from users' PCs.
Microsoft announced in November that it will launch Morro in this month, at which time it will discontinue the $49.95-per-year OneCare service. As of Thursday, Microsoft was still selling OneCare subscriptions. Morro will be compatible with Windows XP, Windows Vista, and the forthcoming Windows 7 operating systems, the company has said.
While users and analysts may welcome Microsoft's offer of free antivirus software, competitors such as Symantec and McAfee and government competition watchdogs may not. Microsoft could draw antitrust complaints if it integrates Morro so tightly into Windows that it makes security software from third parties difficult to install or use.
European antitrust authorities have previously slapped Microsoft with more than $1 billion in fines, in part for bundling Windows Media Player with the Windows operating system.
Microsoft was ultimately ordered to produce a version of Windows for the European market that does not include WMP.