There's a lot of people with the idea that open source can't be secure because people see the source code.
But imagine this. You have 2 locks, one that is completely viewable of the innerworkings, and another that is covered, both have been unbreakable, but could you imagine the balls on the guy that made the clear lock? Imagine feeling so confident that your lock was clearly the best, that you just expose it to any hacker ever and they still can't get in.
Microsoft can barely get things working with their closed source code.
In reality, anything is exploitable and hackable eventually. With the open source community there are so many eyes on it that when someone notices that the program is running 2 seconds slower than it used to, they discover a vulnerability instead of just accepting it and saying "probably MS doing some BS" and dealing with it.