free to download, i use avast. its security but it does not replace common sense. helps when i am trying to find info for a paper and catch one of those interesting links. to lock the sites for free i would use the firewall settings. but i would only allow access to sites that i had approved.

if you are looking for a better firewall than the tissue paper windows version i would look here and search for "firewall" its free.

standard disclaimer. not affiliated. just am happy with the site.