The number of software vulnerabilities discovered last year dropped last year after several years of growth.

But although the absolute number of software bugs unearthed last year slipped by 5.4 per cent compared to 2006, the number of high-priority vulnerabilities increased by 28 per cent, according to a preliminary analysis of bugs by the X-Force group in IBM's ISS security division. By comparison, the volume of vulnerabilities discovered in the previous two years increased by 41 per cent year-on-year.

"2005 and 2006 saw large spikes in vulnerability growth (approximately 41 per cent each year) that were well above the X-Force Database historical average (27 per cent a year). The drop [in 2007] could represent an anomaly, a statistical correction or a new trend in the amount of disclosures," X-Force researchers note.

X-Force researchers reckon the increased percentage of high-impact vulns among the smaller sample may be due to researchers focusing on finding more difficult, high-priority bugs.

Although X-Force's findings are open to different interpretations they do fall in line with findings from Microsoft published last October, looking at the first half of 2007. The software giant noted a drop in the number of vulnerabilities in the first half of 2007 along with a rise in the prevalence of critical flaws among that reduced number. Microsoft's analysis - based on data from the National Vulnerability Database - found a five per cent drop in vulnerability numbers in 1H07 to around 3,600 bugs for the first six months of last year. ®

Related stories

• Attackers hose down Microsoft's Jet DB Engine (26 March 2008)
• A glitch in the Matrix, or a hungry exploit? (30 June 2007)
• VXers suffering from 'writer's block' (21 November 2006)
• Web viruses drop off despite IE exploit flap (18 October 2006)
• Researchers look to predict software flaws (10 July 2006)
• Malware potency increases as numbers drop (25 January 2006)
• Patchy response to reducing security exposure (21 November 2005)