My internet provider doesn't let me open my ports, it's an optional service, and even when they finally said over the phone that I was allowed to open the ports I was still not able to. So I was annoyed with this and decided to set up the raspberry in DMZ to test whether the VPN server I was setting up was configured right or if it was just a port problem. When I figured out that it was just a port problem I fell asleep, the next day I woke up with my username and password changed. Now I'd really like to know whether I was hacked and if so if it is possible backtrack who hacked me. I'm not sure how to do this. I really want to do it just for the sake of it and to gain some experience in this field, not sure if this is dangerous. Of course I changed the SD card of the Raspberry Pi.