From https://answers.yahoo.com/question/index?qid=20071026124052AATbZpO
This isn't a project you would write with PHP. You would need to use a higher level language such as C or C++. Something compiled that will be much faster and more robust then PHP. You can power your web based front end with PHP (i.e. user control panel) but the backend stuff, including payment processing, will need to be in the higher level language. You'll also need an enterprise level database as open source databases could never handle a task like this. Basically...
