Nmap

nmap ,by far is the best security scanning and hacking tool ever made. This software tops every list of top hacking softwares for its two reasons. Firstly,its ease of use and secondly,its wide usage
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It provides a wide range of features like port scanning, fingureprinting, os detection , ping , scanning an IP range , alive hosts etc. It has a rich command mode for advanced users which can combine several commands together to execute ones. Its the most recomended tool for new as well as advanced learners and security experts. It hosts its google  opensource project every year.                                      

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