Microsoft Internet Explorer exploits represented the highest number of hacking attacks in the first half of the year.
According to security company ScanSafe, the number one hack in the second quarter was Exploit.HTML.Mht, which was used to target almost twice as many organisations as other exploits.
"One of the things we've been surprised at is the growth rate of threats," said Roy Tuvey, director of ScanSafe. "There's been a 15 percent rise every quarter and the threat is really rising. The first thing exploited are browser vulnerabilities."
Oddly, 21 percent of virus attacks occurred on Wednesdays and only 6 percent at the weekend. The company said the reason was that most viruses were launched at weekends and spread during the week.
Researchers at the managed Web security company found that while Trojans and worms posed a significant threat, exploits accounted for 19 percent of all attacks they saw. But spyware only totalled 12 percent.
The company also found that ten percent of attacks occurred on email Web sites.
ScanSafe said it receives more than one billion Web requests per month.