Thieves will be thieves. Open source does not stop evil.
If you are talking of kiddies cracking your wifi router, then it's probably just because you either set it up wrong OR the router itself is a piece of trash and has vulnerabilities they exploit.
General advice is, set encryption to WPA2, use 30-char-long passwords composed by random letters, numbers and symbols, turn off the feature called WPS or Wifi Protected Setup which is a known vulnerability (some routers can't disable it or even if you disable it they still leave it enabled). And of course do the same for the router's password.
More extreme measures would be to turn off the DHCP server feature of the router and set up fixed IP addresses for all your stuff. This way anything not using a known device to connect to the router will be rejected.
For more serious needs, Kali Linux is a distro focused on pen-testing I sometimes use to show how bad is someone's setup, it's the successor of the well-known Backtrack, and probably the same distro the kiddies are using to crack your stuff. http://www.kali.org/
their forums (where you can find better advice) are here http://forums.kali.org/
Googling "kali linux crack wifi" will yeld tons of tutorials, so it does not take a genius to use it (which makes it easier to defend against most such attempts).