The email is well designed and, at first glance, does seem like it might be legitimate, but the threatening tone and the lousy spelling should make recipients suspicious.
Still, there are always inexperienced users that can be tricked into clicking on the "Print the invoice" link. Those that do will be taken to a website from which the INVOICE_FORM.zip file (containing an executable of the same name) will be downloaded.
Unfortunately, the file is not a form, but a downloader Trojan that is currently detected by less than half of the AV solutions used by VirusTotal.
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