What do you mean by 'security breach'?

Thanks David for your interest in my problem. Perhaps security breach the wrong description, I mean Thunderbird is attaching the complete file (multiple worksheets and correspondence)from where the Excel spreadsheet I want too send is saved, the receiver is obtaining access to all my confidential information in that file, which perhaps could lead to being illegally used for what ever they wish for example; identity theft etc.

Does this happen every time? I ask, because it's easy to accidentally highlight more than one file. I have never had a similar problem reported. Please share more on the frequency of this and whether it just started.

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