Whether you wish to be a hacker who is interested in hacking wireless network, web app, database; cracking password, software....; or want to engage in cyber security related works in the future, Offensive Security's Kali Linux (a penetration testing OS) should be always your main "battlefield" and "experimental field".
Without any doubt, Wireshark (formerly called Ethereal) is currently the world's most famous, foremost free and open source network packets capture & analysis tool. Its appearance puts an end to the future of all similar business software.
Good, convenient things will always be popular, get more attention from users, and followed by exposing more problems. The wireless network is one of such new things, which began to catch on around the world due to its application on mobile platform.
Today, wireless network has got very extensive application because of its convenient use and structure, and will eventually cover every corner on the earth, I believe. But due to its broadcast form of data transmission in a wireless network environment, that will inevitably lead to security issues. Of course we can ensure data security by setting different encryption methods in a wireless router, but some loopholes of Wi-Fi network or the router itself can often make every trained hacker be able to crack/hack it.