Symantec is the second antivirus vendor to cripple or damage Windows systems with a flawed update in the last two months.
In mid-May, German security company Avira released a buggy signature update to its behavioral-based monitoring system that blocked virtually every legitimate Windows executable file -- those with the ".exe" extension -- and prevented applications from launching.
Nearly every major antivirus software supplier -- including McAfee, Microsoft, Symantec and Trend Micro -- have shipped defective definitions. In some cases, those mistakes have wreaked as much or more havoc as the latest blunder by Symantec.
According to security vendor Opswat, which reports on usage share every quarter, Symantec accounted for 15.1% of the all operating antivirus products in North American as of June -- second behind Microsoft's 22% -- and 10.3% globally, for the fourth spot after Avast, Microsoft and ESET.
In light of the blue screens, Symantec said it was revamping its quality assurance testing process "to improve compatibility testing" and would hold off any future SONAR signature updates until the new procedures were in place.
A document on Symantec's website describes the issue and offers a workaround.
Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer, on Google+ or subscribe to Gregg's RSS feed. His email address is email@example.com.
Read more about windows in Computerworld's Windows Topic Center.