I posted some info on C and C++ in one of my posts. You can try the following
programming links like:

www.cprogramming.com
http://www.cs.wustl.edu/~schmidt/C++/
http://www.vb-bookmark.com/CppTutorial.html [This is a good one.]
http://www.programmingtutorials.com/main.asp [this is also a good tut.]

and the list goes on...

Online games are mostly made in Java, Flash and other formats and programming languages. It is seldomly made in C++. Java is very secure because it is made keeping the 'Internet' in mind. However, there might be some vulnerabilities and flaws in some online games. You can search for 'Online Games Vulnerabilities' in Google. You will find many patches and solutions that would eliminate some flaws. I will try to find out more info on this.

I hope that answers some of your queries.