Zero-day web-based malware attacks, the company said, accounted for almost 90% of all threats.

ScanSafe reported that it blocked 36% more malware in Q2 this year than the previous quarter,

The notorious Gumblar botnet was the single biggest contributor to this malware rise, with 14% of all web malware encounters in the quarter being the result of encounters with Gumblar-compromised sites.

"The fact that the most serious threat of the year was not detectable by most standard anti-virus signatures should serve as yet another wake up call to the security community," said Mary Landesman, senior security researcher with ScanSafe.

"The evasiveness and sophistication of the Gumblar threat has set quite a precedent for threats to come. Companies need to be prepared with a comprehensive web security solution - specifically, a solution that adequately protects against the increasing rate of zero day threats," she added.

According to ScanSafe, the second quarter of 2009 also demonstrated a sharp increase in data theft trojans.

The rate of encounters with data theft trojans increased 37% in 2Q09, the firm said, adding that the most prevalent of these encounters were with Backdoor trojans, which can lead to data theft, registry manipulation and full control of files on an infected system, amongst other things, said Landesman.

"It is alarming that the prevalence of data theft trojans has increased so significantly this quarter, but not surprising," she said.

"Stolen data is in high demand and in this economy cybercriminals are motivated to develop increasingly sophisticated tactics to obtain that data," she added.