Should it be open source or are you going to trust that there is no back door implemented somewhere to sneak in later when there are some serious volumes and amounts? I have a feeling that all the hacking cases were just like this one, some body bought a ready platform from a coder, programmer and that coder either himself attempted the hack or leaked some information, I'd suggest to be extremely careful when it comes to trusting programmers as most of the skillful and hard core coders are also involved with hacker communities, there are some open source platforms which are free obviously in GitHub, all you need is to search in there and after finding what you are looking for all you'd need is to upload the files in to your servers and domain.