I get this message when ending tasks in System Monitor:
I understand ending processes will remove data in memory and break its current session, but how can ending a process create a security risk??
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It may introduce a risk if the process is not allowed to perform necessary clean-up.
For example, when a text file is edited, the new contents are often stored in
/tmp, or even in the current directory, with an obscure filename. This file is simply renamed as the original file when the user saves to disk, or deleted when the user discards the edit.
If the process is not allowed to either rename or delete, there is a security risk if the original file, or the unsaved edits, contain sensitive information, like passwords.
Now extend the analogy to web browsers and session cookies, and you have a formidable security risk.
Edit: As pointed out below, properly coded programs will take due care to ensure that a forced termination does not become a security risk.
However, not all programs are properly coded and the O_TMPFILE mechanism was added in Linux 3.11, so code written prior to the addition will not make use of it. That includes the current LTS, which is stuck on Linux 3.8.
It is best to assume that a program will cause a security risk if forcefully terminated, unless you have had the time to inspect the source yourself.