See
here. I wonder what security they're talking about. Job security? Most likely. Proprietary software as security for customer retention? Probably. Obviously this is one of the people who deny useful practices like security audits (which is obviously done by everyone who wants to use Linux in
really security-critical environments), who have been done a lot of times for all the critical Linux code (including userland) in the past years. Since software can practically never be bug-free (well, except for toy programs), Linux has bugs, too. But due to the security audits and code reviews, the most obvious and even several not-so-obvious bugs and actual security holes could be found and removed. And this is what still has to be done for proprietary software, which often enough suffers from simple buffer overflows and string format attacks (muhahaha, this is a problem practically non-existant for free and open-source software, because it is easy to find and fix when you have the source).