Users of Check Point Software's ZoneAlarm personal firewall products can now download a fix that resolves an Internet connectivity glitch created by a Microsoft security patch released earlier this week.

The fix applies to the ZoneAlarm Internet Security Suite, Pro, Antivirus, Anti-Spyware and Basic Firewall editions of the product. It can be downloaded directly from Check Point's ZoneAlarm.com Web site.

The problem began on Tuesday when Microsoft sent patch number KB951748 to Windows users. The patch is designed to plug a security vulnerability that leaves computers vulnerable to so-called DNS attacks.

The vulnerability is widespread and affects products made by numerous networking and software vendors beyond Microsoft. It was discovered by Dan Kaminsky, of the Seattle-based security firm IOActive, Inc.

Through a DNS attack, a hacker can redirect Internet users' page requests to phishing sites or other malicious pages. Various reports suggest that ZoneAlarm interpreted the Microsoft patch itself as malicious code, and automatically severed users' Internet connections in response.

News of the trouble spread quickly on Internet forums.

"For those of you using ZoneAlarm who installed the Windows updates today, you probably already know that your Internet connection has died," wrote user "Winchester73", in a post Tuesday on the popular broadband forum DSLreports.com.

Numerous other forum users reported experiencing the same problem. Dozens of posters on ZoneAlarm's own forum reported Internet outages. "I service and administer approximately 200 privately owned computers and I have received about 20+ telephone calls from users with this problem today," wrote "Calken".

To download the ZoneAlarm patch, users may first have to uninstall the Microsoft patch in order to restore their Internet connections. CheckPoint said lowering ZoneAlarm's security settings to "medium" might also restore connections even if the Microsoft patch is still present.