to the casual observer, yes it appears pretty insecure. once you try to hack it, then you see the genius of the design.
There is nothing genius about the code, and nothing genius about you.
other than the queries, i'd say its pretty secure.
Your opinion means nothing and is apparently given out without any thought. That code is some of the worst I've seen in years. WTF makes total amateurs think they can launch an exchange that's responsible for handling people's money? Based on that code you're about 5 years of programming experience away from being able to, possibly, code securely enough. Don't even think about relaunching with anything but a play site.