Go into many small or midsize companies, and you may find a Linux firewall churning away in the computer room, keeping out bad packets and letting in good traffic. Businesses often choose Linux firewalls for their reliability and low cost, compared to products from Cisco or NetScreen that can cost thousands of dollars.But Linux as a firewall platform also catching on in larger firms. One financial services company is using 10 Linux firewalls in one of its data centers."We're using Linux as our security platform as a way to keep costs down," says the firm's network administrator, who now oversees the network security and requested anonymity.The admin says his firm had used firewall appliances, and even Unix servers to run firewall software. But when organization's budget was tightened he decided to switch to Linux and Intel servers, which were cheaper to deploy and maintain than the Sun and IBM RS6000 boxes he'd used previously.The company uses Intel-based servers running Red Hat Linux, which includes a firewall software package. The boxes are reliable protectors of the company's trading data center, which executes online orders for the front-end Web site of a major online trading firm."We have some pretty important information being protected by those Linux boxes," the admin says.