recieving empty attachments on the hotmail

I 'm receiving e-mails from a certain friend on the hotmail , that contain empty attachments, one of them had an image attachment called image001.jpg and its size is 0.2 kb and when I opened this photo it was empty a blank white page, I received this empty attachment several times from the same friend, and once he sent me an e-mail, containing the attachment sign in it’s title (before opening the e-mail) but when I opened the e-mail there wasn’t any attachmentas signs nor attachments inside the e-mail.
Is this some kind of hacking or spying or is it a virus or is it something else?
sorry for the elongation and thanks :slight_smile: