Linux security is a myth. You’ll never convince me that an OS where everyone can get the source code is more secure than a proprietary one. It’s a good bet that the hackers that try to bring down Windows are Linux junkies and all hate Bill Gates. If they turn on each other we will see just how secure Linux isn’t.
Here's the source code to TripleDES, which hasn't been broken. It's a highly regarded encryption algorithm. It's publicly available, yet unbroken.
There are many reasons that Linux is more secure than Windows. The fact that the source code is probably easier to get at (because you can get access to both) is one of them. More people looking for errors mean more people finding them and pointing them out. Most people who are into that sort of thing would like to contribute, and they also get off on getting the credit for finding a problem.
Same thing goes for encryption schemes. The ones that are well known and documented tend to be more secure than those that aren’t. Actually, try to keep the algorithm secret and no one will use it (of course, they’ll break it just to show you that you’re being an idiot trying to implement “security by obscurity”).
There really aren’t a lot of things people would want to do with a “cracked” computer, other than just the challenge of doing it. Given that, what would most people do if they found a hole?