The crashes happened after people downloaded the daily Program Advisor update, said Gregor Freund, general manager of Zone Labs, which is. Thursday's update contained a bug that had slipped by Zone Labs' quality checks.
"There was somewhat of a process breakdown," Freund said on Friday.
The Program Advisor update is a list of trusted programs that tells the firewall which applications should be allowed to connect to the Internet without user interaction. A new version of the list is produced daily. By default, ZoneAlarm products check on start-up for a new version and download and install it, Freund said.
Most customers who experienced the crashes were in Asia, because it was morning there when the update was first made available and users were starting up their PCs, Freund said. About 50,000 users experienced crashes, he added. About 3 million people use ZoneAlarm Pro and ZoneAlarm Security Suite worldwide, according to ZoneLabs's figures.
The faulty update was made available around 4 p.m. Pacific Time on Thursday. Zone Labs discovered the issue after customers began reporting crashes. The problem was replicated in the software maker's security lab and resolved within five hours, according to a posting on Zone Labs' Web site.
The company late Thursday posted a corrected Program Advisor update. Customers who rebooted their PCs automatically received that new version, Freund said.
The issue affected only the commercial ZoneAlarm Pro and ZoneAlarm Security Suite, he added. The free ZoneAlarm firewall does not include the Program Advisor feature and was thus not affected, he said.