Software giant Microsoft Corp is to launch a free PC security service this week, in what could be the biggest challenge to date for anti-virus companies with billions of dollars in annual revenue.
Microsoft Security Essentials offers protection from several types of malicious software, including viruses, spyware, trojans and rootkits.
If its scanner detects a suspicious file that is not yet registered as malware, the programme alerts Microsoft researchers for further investigation.
Executives from internet security companies Symantec and McAfee dismiss it as a lightweight alternative to full protection that they offer in their top-selling security suites.
Microsoft's offering fights only malicious software while the best-selling products from security rivals bundle in other features such as encryption, firewalls, data backup and parental controls.
Microsoft says a beta version of the product will be available for download on its website on 23 June and a final version is planned for later in the year.
The free service comes after a botched attempt to sell a suite of security software dubbed Live OneCare that Microsoft launched three years ago. It announced plans to kill that product in November.
