Why does my computer send any network data, even if I am not doing anything?
Is it possible that this network traffic includes private data (text documents, images,...), to which I did not consent?
Information Security Stack Exchange is a question and answer site for information security professionals. It only takes a minute to sign up.Sign up to join this community
I'm going to assume you ask why you see traffic on your machine, even though you don't actively do anything. The reasons for that are that your computer is doing a lot in the background, which is not triggered by any user action. Let me give a few examples:
Of course, there are many more reasons why your computer may show traffic, even if you're not "doing anything".
Could these contain private information without my consent?
That depends what you consider private information. For example, Firefox sends requests to fetch
http://detectportal.firefox.com/success.txt. An attacker in the same network could listen to this request and detect that you are using Firefox.
As far as your consent goes, it depends on the Terms of Service of each individual application. You would be surprised to what things you consent just by using regular applications.
Could these replies contain personal documents?
Answering a comment, usually no. Of course, if you use a file-sync service such as Google Drive, Dropbox, etc., it is of course possible that personal files will be included in such traffic, but this is by design.
As for other applications, it would be highly unlikely. For example, if you bought a video game from Steam and it would suddenly send copies of all your files to the publisher, such a case would become popular very quickly and would put the developer into hot water (and likely get their game banned from Steam quickly).