For many years now, open-source software has been used for mission critical tasks in Internet and Intranet. Linux and FreeBSD are used as the operating systems for even the most demanding sites, such as Yahoo, and often out-perform their commercial equivalents.
Open source is ready for the enterprise.
Open source software has a long tradition in IT security - where reliability, flexibility, transparency and trust are vital. Security software must be reliable and without vulnerabilities like buffer overflows. The only economic way to look for such flaws is by checking the source code. That's exactly what some code audit projects are doing. They check the source code of application programs and even complete operating systems, line by line and eliminate security flaws.