I get 'DE:AD:C0:DE:CA:FE' on my network
You have not been hacked.
Since version 1.10.9, Fing has added a 'DHCP server Finder' inside the Fingbox. This discovers every active DHCP server inside the network by sending a fake request with the special MAC address 'DE:AD:C0:DE:CA:FE', which may be recorded as a new device by your router.
Knowing the list of active DHCP servers helps to troubleshoot specific issues, and is considered standard practice for performing this type of test.
Click the Submit a request button at the top right of the page