This is more a philosophical question but its one I've been pondering for some time now.
I don't know anything about computer security or how computers are broken into. I thought hackers used disassembling software on executable software to create malware and other things.
My question is would making some software open source make it vulnerable to hackers or do I have reverse engineering confused with hacking?
Making something open source does not inherently make it more vulnerable. Trying to hide what you are doing is known as Security Through Obscurity, and it doesn't work very well.
Making something open source makes things easier for casual hackers, since they can see how your app works more easily. On the other hand, making it open source also lets anyone who is interested look through your code and report security vulnerabilities. They're two sides of the same coin.
For the most advanced threats, they'll get through regardless of whether your code is open source or not. On the other hand, honest volunteers are much less likely to bother trying to find and fix bugs in a closed source product.
So basically, it depends. In general, you're better off open sourcing things if you think people are actually going to be interested in the project.