According to Web security vendor Dasient, a number of 1.3 million Web sites were infected by almost 200,000 different threats during Q2 2010.
"This quarter marks a significant spike in the number of infected websites - almost double the number of the previous quarter.
"Hackers have been very busy and are constantly coming up with new attacks," the vendor writes in its latest quarterly report.
In addition, the company points out that this is the first quarter when the number of infected websites has passed the one million mark.
"Scripts sourced in via IFRAMEs, by comparison, do not have the capability to access or communicate with the rest of the page," the Dasient researchers explain.
The number of attacks that involve malicious advertisements was also on the rise. The company estimates that 1.6 million malvertisements are served on a daily basis, which is an increase of 20% over a mid-Q2 estimate.
In addition, the lifespan of malvertizing campaigns has increased by over 50% and is now 11.5 days. A tendency to launch such attacks during weekends has also been observed.
A noteworthy increase in the number of .info malicious domains was also recorded, however .com and .cn remain the TLDs preferred by attackers.