Ad server needed

I need a simple adserver that can host different websites. It must be in core php and installed on our server. The code must be made so that it is easy to add code without rewrite the code totally. It must be verry secure for any attacks. The paymet is via PayPal for the customer. It must also make a montly report that can be accessed trough the admin area. There must also be an option to automatically transfear the funds to our bank and send an invoice to our mail with the amount transfeard. There must also be an option to set % VAT to the prices, and get that spesefied on the invoice. The adserver must hadle txt and multimedia ads.