[Observium] Auto Discovered Device

Hi All

In my Observium installation there is a new Device named "core" appearing every 6h (expect from the discover process) after 12h I have two of them and so on. If I delete them the reappear. I do not know from where this comes. Is there any way to find out how observium finds this device?

If not, what's the best way to prevent Observium from automatically adding new devices ?

Regards

Matthias