Microsoft Corp is getting ready to unveil a long-anticipated free anti-virus service for PCs that will compete with products sold by Symantec Corp and McAfee Inc.

A Microsoft spokesman said on Wednesday that the world's biggest software maker is now testing an early version of the product with its own employees and that it will soon make a trial version available via its website.

Shares of Symantec and McAfee, the top two makers of security software, tumbled in November after Microsoft disclosed plans to launch the service as investors worried that they will lose sales to the free product.

Microsoft has said that it will only include basic features for fighting viruses, which would likely make it comparable to the least-expensive products sold by Symantec and McAfee.

Their top selling products are security suites that come with features include encryption, firewalls, password protection, parental controls and data backup.

(Reporting by Jim Finkle; Editing by Steve Orlofsky)