Web Shield : block domain .tk

Hi,

We received some SPAM with links to dangerous Websites .tk.
I’m trying to block all sites with .tk domain using Site Blocking and filter http?://www..tk but it seems not working (I can still access to http://www.dot.tk/)

Do you think is it possible and how should I configure Web Shield ?

Thanks

Hello,
I don’t know if this would work for you, but I block downloads of certain files like this: http://.exe
Maybe you can try http://
.tk