Zone Labs, the San Francisco-based company that has popularized "personal firewalls" by giving them away, announced a big win yesterday. The company has teamed with Cisco, contributing its software to the latter's Cisco VPN Client version 3.5 software.

Personal firewalls protect a desktop computer from hacker attacks by monitoring connections to and from the Internet. They're particularly useful on PCs connected to a virtual private network (VPN), because viruses or Trojan horses might travel over the VPN and infect a corporate network.

"Without malicious intent, employees may inadvertently subvert enterprise security policies, and thus expose the entire corporate network to infiltration by hackers via the Internet," says Pete Lindstrom, director, Security Strategies, Hurwitz Group. "This joint solution from Cisco and Zone Labs raises the bar on enterprise security by ensuring that all endpoints are secure prior to network connection."

The Zone Labs "cooperative enforcement technology" featured in the VPN client can be configured on a spectrum from "permissive" to "paranoid" to fit the enterprise security policy. At its most paranoid setting, the technology ensures that no VPN connections are made without the Zone Labs personal firewall running on the client, and an appropriate firewall policy being applied.

Zone Labs does relatively little advertising, but has received high ratings in the press for its firewall software. Users who download free software from Zone Labs can upgrade to the ZoneAlarm Pro product for $40.

The alliance with Cisco is the second time Zone Labs has teamed with a hardware vendor. Earlier this year, the company allied with Linksys, the Irvine, Calif.-based manufacturer of routers for home networks.