Hi all I'm new to the forum, I just bought an iMac online, but it says powered by some company and it keeps asking for a login after I formatted and reinstalled the OS system. What do I need to do to make it my own?
Depending on how and from whom you have purchased & availability of the full package e.g papers, charger, box, etc.
Apple Support (official or relative to one) can help you to remove MDM profile but obviously, there is no guarantee
Contact the seller.
If they sold you a used Mac that came "loaded" with an MDM, then the seller should either help with removing the MDM profile, or replacing that iMac with one that you can actually use.
OP did not mention eBay, but certainly contact the seller.
Point well taken about buying from a reliable source.
The previous owner certainly made no effort to prepare that iMac for sale.
Unfortunately there seems to be a thread like this just about every month: someone buys a Mac online for "a great deal," it turns out to have MDM because it is actually stolen or "fell off a truck," the seller disappears, and it is impossible to remove the MDM without the cooperation of the company from whose truck it fell off.
Either that, or trying to find a way to make a Mac more sellable.