You should never be generating a wallet, paper or otherwise, on a device with internet access enabled, for this very reason. The correct way to generate a paper wallet with bitaddress is to download the site, verify your download, and then transfer it using removable media such as a USB drive to a permanently airgapped machine running a totally clean OS. Most users would use a live OS such as Tails or another Linux distro.
This. I can't stress this enough. People have been heavily recommending paper wallets to people left and right without even mentioning the risks of making a paper wallet on a typical personal computer. The paper wallet itself sure is offline, but the process of making one is definitely not offline unless you take the extra safety precautionary measures mentioned by o_e_l_e_o. Simply turning off your computer's internet connection when generating a paper wallet really isn't enough.