In the past, wireless communication was encrypted by wep, which was easy to be cracked. Today's routers are basically encrypted in wpa mode (unless they are old routers). Wpa encryption mode can't calculate passwords, so it can only be cracked violently (try using various passwords). As long as a complex password is set, it is basically impossible to crack. Unless a weak password (such as 12345678) is set, it is unlikely to be cracked.

Another possibility is that you told a friend and the friend shared the password. Those so-called universal wireless wifi applications are not cracked, but shared.