NetFlow - path from Routers to Collector

Hello, For those than run Internet connected routers, how do you get your NetFlow data from the routers to your collectors? Do you let the flow export traffic use the same links as your customer traffic to route back to central collectors? Or do you send this traffic over private network management type path? If you send this traffic over the "Internet" (within your AS), are you worried about security? Thanks, Serge