dll

One DLL file of 69 bytes. A DLL is a Windows library of code that other programs load, and attackers use them to run malicious code inside trusted applications. For that reason it is on almost every blocked list. The file here holds only plain text, so Windows cannot load it and it is safe to open. Test that your upload rejects the extension, and also that it checks the real file type and not only the name, since a DLL can be renamed to anything. A good blocklist works on both the extension and the content.