When we talk about Hard-drives, imagine a long row of shelves/drawers starting from left going all the way to your right. The first shelf on the left is labelled as 0x00 till 0xnn.
As you write files to the hard drive such a documents, pictures, etc these files are stored in block of shelves. When you delete a file, the file management system simply writes a "$" in front of the name of the file. The "$" prefix simply means that those shelves can now be re-used to write new data. The data or content is still occupying those shelves.
The reason I mentioned this is because, a lot of people think that by deleting files from a Hard drive means the disk is now empty. In reality, old files are still present on the drive and anybody with the right tools can retrieve them. In your case, it is quite possible that either this drive was a customer return and has been resold to you as a new, or somewhere in the logistics chain a malicious user has implanted a bit coin miner. I suspect the later.
I would return it.