Microsoft is failing to confront an increased number of critical vulnerabilities in its software, according to data collected by security vendor McAfee. 

The software giant patched 36 critical holes in its products in the first five months of 2006, marking a 70 per cent increase over the same period last year. 

Microsoft insisted in an emailed statement to vnunet.com that it does not believe the increase signals an upward trend. 

"There is no real significance to be placed in such a small sample set as January-June 2005 and January-June 2006," the firm said.

Microsoft added that it aims to reduce the number of vulnerabilities in its software, and has succeeded in several of its products including Windows Server 2003 and SQL Server 2005.

The company dismissed speculation that bug bounty programmes from security vendors like iDefense and TippingPoint play a part in the increased number of flaws found in Microsoft products.

IDefense organises quarterly challenges in which bug hunters can earn $10,000 if they report a critical vulnerability. The company targeted Microsoft products in the first quarter of this year. A contest going after databases is to conclude at the end of this month.

The iDefense contest resulted in the largest number of bug submissions in the history of the programme, a spokesman for iDefense told vnunet.com, three of which were patched by Microsoft last week.

The company paid the $10,000 bounty to the individual who found a critical flaw in the ART image file format.

IDefense agreed with Microsoft, however, maintaining that it is too early to draw any conclusions about the significance of the increase in security bugs in Microsoft software.

TippingPoint and iDefense are the only known commercial security vendors offering money for information about unpatched security vulnerabilities.

But it is believed that there is a large underground market for such information in which criminals, government spying agencies and corporate espionage groups bid against each other for zero-day exploits.