Web-based malware surged by over a third in the last quarter with zero-day attacks now comprising nearly 90 per cent of all threats, according to the latest report from security-as-a-service provider ScanSafe released today.

The firm said it blocked 36 per cent more malware in Q2 this year than the previous quarter, which equates to an average of 4,575 malware encounters per customer.

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

The number of data theft Trojans also jumped sharply in the last quarter – by 37 per cent – with the majority being variants of Backdoor.Bifrose, a family of stealthy Trojans that inject a backdoor into the browser process, according to ScanSafe.

“It is alarming that the prevalence of data-theft Trojans has increased so significantly this quarter, but not surprising,” said senior security researcher Mary Landesman.

“Stolen data is in high demand and in this economy cyber criminals are motivated to develop increasingly sophisticated tactics to obtain it.”