hacking is an incorrect term unless you were using WEP/WPA1/WPA2(with a vulnerability of router/modem model) with password & someone used a tool to crack your password to gain access.Since so many ppl were connected my guess is either password was not there or password was leaked by someone who already knew the password(your friend told his friend & so on in the colony).
The most logical and plausible reason.
[MENTION=159396]aal-ok[/MENTION], In fact I have a very strong password of alphanumeric + spl. characters of length more than 20 as a password for my wifi setup(also as hotspot setup) in my home.
I am not saying that the password won't be vulnerable,but it will take a very hard time to crack with even specialized softwares. [MENTION=126812]whitestar_999[/MENTION],could throw some more light on this,being a network expert himself.