Ensure you are using the latest version of WinRAR (at least 6.23 or newer) to patch known vulnerabilities.
This technique uses a special hidden Unicode character to flip the order of characters in a filename. For example, a file named report_txt.exe can be made to appear as report_exe.txt to the user, masking its true executable nature.
In Windows File Explorer, go to the "View" tab and check "File name extensions" so you can see the true nature of every file.
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