Testing software for Security is something that can be quite complicated to do. Those that do test software are also those that have taken classes and know just what it is that they are doing.
If you are all into software, and are very familiar with it, as well as interested in testing it yourself, you are going to want to check out the software testing course that is held closest to you.
Many companies hire a 3rd party to give their employees a security testing course or build an in house team for providing this as a special service to teams across the organization.
I somehow believe that Security testing is something that comes a little easier to someone that understands or has written a software program before. If you have ever written a software application and are looking to get into testing, you are going to find that learning what you need to know to test will be easier for you than someone else.