Check Point Software yesterday launched a Windows Vista version of its ZoneAlarm firewall. Check Point also announced a Vista version of its ZoneAlarm Internet Security Suite. Customers with current subscriptions to earlier editions can update to the Vista version free of charge.

The Vista version of ZoneAlarm, a two-way firewall that will remain free, is the first from a major security vendor to apply Vista's WFP (Windows Filtering Platform) API (application programming interface), said Laura Yecies, the general manager of Check Point's consumer security line.

Yecies blamed the delay in the release of a Vista-compatible ZoneAlarm on a switch to Vista's API. "This is a bit later than we would have liked," said Yecies, noting the four-month lag between Vista's retail release and ZoneAlarm's appearance.

WFP is Vista architecture that lets developers tap into the TCP/IP processing path. but, according to Yecies, it was a steep learning curve. Microsoft used WFP to create its own Windows Firewall, which is bundled with Vista.

"We underestimated the schedule impact of WFP. But long term, WFP will give us more support and more stability on Vista. It was a lot of extra work, but we'll have to do fewer hacks in the future."

"At times, it seemed like we were an extension of Microsoft QA. They patched and made changes based on what we found while we were developing," Yecies said.

But Check Point remains committed to keeping ZoneAlarm a free download.

"It's very important to who were are," Yecies said. Zone Labs, which was acquired by Check Point in 2004, made its name by giving away the firewall. "And we think it's the right thing to do," she said. "Our paid users live in a safer world because there are 20 million more protected by the free firewall."

Check Point touted ZoneAlarm, also the foundation of the ZoneAlarm Internet Suite that was released yesterday for Vista, as an "operating system-level" firewall.

"Eighteen months ago, we decided that the firewall had to operate at the lowest level of the OS, to monitor every call, every program," said Jordy Berson, ZoneAlarm product manager.

"There are so many new threats that we need a behavioural-based firewall" to detect and defeat more insidious attackers, including rootkits and drive by-installed keyloggers, Berson said.

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"ZoneAlarm does for the computer itself what it was already doing for the network," she said. The Vista firewall tracks 30 different behaviours, such as API calling, logging keystrokes or injecting code, then decides if what it's seeing is safe. If not, it shuts down the process in the same way as a more traditional firewall shuts down access to the internet when it spots a rogue.

More: Microsoft prepares for Windows Vista SP1

ZoneAlarm's delay had nothing to do with the brouhaha last year over access to the kernel in the 64bit version of Vista, Yecies said. Last autumn several security vendors including Check Point rivals Symantec and McAfee pressed Microsoft to back off its PatchGuard kernel-protection technology. Eventually, Microsoft agreed. In December, Microsoft released draft APIs.

"Interesting questions, but it was a separate issue," said Yecies, who then launched into criticism of PatchGuard and Microsoft's APIs.

"They won't solve the problem [of hackers cracking the kernel]," she said. "If there is some new unknown threat in the future, the APIs won't help you. [Microsoft] would need to react, update and distribute the APIs to millions."

Yecies drew a line in the sand. "We're going to do whatever it takes to protect customers, even if it means hacking PatchGuard."

The free ZoneAlarm firewall is available for download from the Check Point site. ZoneAlarm Internet Security Suite 7.1, priced at $39 (£21) is also available.