Microsoft (17.07 percent), AVG (15.63 percent), and Symantec (14.47 percent) were found to be the top three antivirus vendors in North America, according to the latest quarterly antivirus market share report released by OPSWAT. Microsoft increased its market share from OPSWAT's previous antivirus report to surpass Symantec and become the North American leader. AVG held steady in the second position, and Symantec fell to third.

Worldwide, the top three antivirus vendors detected were Avast (12.37 percent), AVG (12.37 percent), and Avira (12.29 percent). Microsoft was fourth (11.24 percent), followed by ESET Software (9.98 percent).

The software company analyzed more than 43,000 opt-in reports from endpoints worldwide. The reports, generated by OPSWAT's AppRemover and Am I OESIS OK? tools, utilize the detection capabilities of the OESIS Framework to list the applications installed on the endpoint computer. The full 8-page document, titled Q2 2011 Antivirus and Instant Messenger Market Share Report, includes data on the leading antivirus vendors and products in North America and worldwide, Windows OS usage in North America and worldwide, instant messaging market share worldwide, and instant messaging usage in North America and Europe.

The rest of the data wasn't too surprising: Windows 7 usage continues to increase in North America and worldwide, showing a steady trend away from Windows Vista. In both North America and worldwide, Windows XP remains the dominant Windows operating system. The top three worldwide IM applications are Windows Live Messenger, Skype, and Yahoo! Messenger. The report does not, however, account for Web-based instant messaging services such as Google Chat or Facebook. This is because it only looks at installed applications, and those services run in the browser.