i have problem in installing aircrack on ubuntu 14.01

My code: sudo apt-get install aircrack-ng

It displays

[sudo] password for user: 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package aircrack-ng is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
However the following packages replace it:
  iw

E: Package 'aircrack-ng' has no installation candidate