Could clicking on an e-mail attachment (a Microsoft Excel file) from a trusted source (work colleague) have installed a tracking virus that would have allowed the sender to obtain browsing history from my computer?

I realise this will raise issues of what I was looking at online and why I feel this may have happened to me. The reason I ask is that I generally would only have used my laptop at weekends generally for online learning etc. Concerns that a work colleague may have been able to access my browsing history arose when conversations at the start of the week were detailed around what I had been looking at online at the weekend - initially minor common themes and then around detailed legislation not specifically related to where I work but that I happened to be looking at that weekend.

Have delayed querying this as I do not wish to appear paranoid but would like to know if this is a possibility and how would I find out for sure?

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Your question is quite vague, but here are some pointers that might be of help:

  • Email attachments are a common method for putting malicious files on your machine, along with drive-by downloads.
  • It's more common to be infected by unknown mail senders or on dubious and unknown websites than by trusted third-parties (except maybe for social network malware which necessarily spreads through your connections)
  • You can still get infected by trusted parties or on trusted websites, if they have been infected themselves
  • From your question I take it that you're more worried about your colleague spying on you. If your colleague is not a trained computer security engineer or hasn't done any hacking in his life you're most likely safe! Indeed I don't think that Excel files are commonly used for extracting browser history (if you wanted that information it'd probably be easier to make you install a malicious browser extension)
  • You must still open these files for them to have any effect. This is in opposition with many Web attacks that run local scripts on your machine simply because you visited the page.
  • App sandboxing is starting to appear on all major desktop platforms, though not fully deployed yet. If you opened a malicious file with an unsandboxed app, and that file was not detected as malicious by the app or your antivirus, virtually anything could happen to your data and the other apps you use.
  • With a sandboxed Office app the damage would very likely be contained to your Office instance and would not have any further consequences. I've heard that nowadays you can run Office files in "Protected View", which only allows you to read them but blocks most potential malware.
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