Yes. You've found out how the version 1 api has been deprecated / is in the process of being removed.
From now on, all your requests to the twitter API will be required to have authentication (OAuth), and for some this was a nightmare to figure out.
Fortunately, I wrote a lengthy post (with pictures) explaining how to set yourself up a twitter dev account / application, get a set of keys, and then I created a library to perform authenticated requests for you.
The only downside is that this library is written in php, and from looking at your profile you use ASP.net - so try googling for a library for your specific language if you don't want to use PHP.
In any case, no more unauthenticated requests for you ;) You need to dig in with OAuth now!