Broadcom Wireless Drivers unclaimed after installing update 16.04
modprobe: ERROR: could not insert 'wl': Required key not available
This is the subject of a recent and still open bug in Ubuntu: https://bugs.launchpad.net/ubuntu/+source/bcmwl/+bug/1572659 Please also see: Can't view Wifi networks after upgrading to Ubuntu 16.04
It appears that the only solution so far is to enter the computer's BIOS and turn off Secure Boot.
Secure Boot is a security standard developed by the PC industry to help make sure that your PC boots using only software that is trusted by the PC manufacturer
1) Turn off the secure boot
2) Remove bcmwl-kernel-source
sudo apt-get purge bcmwl-kernel-source
3) Re-install bcmwl-kernel-source .
sudo apt-get update sudo apt-get install bcmwl-kernel-source
Reboot. Your wireless should now be working.