IIRC the attachments in my example didn't have fake extensions, because I could easily open them in the respective programs - after the antivirus had deleted the malware, of course. Back then, about ten years ago, it was quite easy... One was .txt, the other was .jpg. The .txt file was, as I told, the last minute additions to Win98 file, the .jpg seemingly was a temporary Internet file. The former mail looked just puzzling, the title and message were in Finnish but had no logic with each other or the attachment. Like if someone erroneously sent you a reply to a question someone else has stated. The other mail I got from the same infection was more clearly generated by a virus: Why would a Finnish guy send me an e-mail written in English, the message being: "Look at my beautiful girlfriend" and the attached .jpg showing two models wearing rainclothes.
Both of the mails claimed to come from people who are in my address book and whom I personally know. Because they aren't my business partners, should their mails be treated as potential threats if I read them on machine? What about the fact that I get most spam to the e-mail address of my firm, provided by my ISP? I wouldn't call "business related affairs" those ads whose source for addresses is the public registry of companies...