I agree, we cannot be too careful. Many of us will not expect to get an Excel spreadsheet in an e-mail, but it is surprising how many people will still open one.
I am wary of any Emails from unknown sources, and delete them without reading.
There are other potentially-dangerous things about, too.
A couple of days ago, Mrs A had a error warning (I forget the number) on her tablet. I Googled it on my laptop and the first thing that came up was a website saying that I could download a free 'something' that would correct this fault. Delving further into it I found that the download would take 'only' 15 minutes. I thought, "No way! Do they think I'm daft". Going back to the Search site I then clicked on a Wikipedia link, that explained that this Error Notice simply meant that the website concerned had closed down or moved. Goodness knows what would have been the consequences if I had let the first website have 15 minutes access to my computer. These rogues should not be allowed.
Aggers and all. There was a time when your browser would throw an error code, but not much else: 400 Bad file request; 404 File not found; 408 Request timeout; 500 Internal server error, and so on.
They were meaningless to most people so newer browsers give a bit more information: See this Unfortunately some of the explanations look a bit dodgy or almost as confusing as the old error codes! Best bet is to close the tab and try again, and if it does not work, give up - as Homer would say.