Preposition Problem

What preposition should I use when we refer to a website? For example:

"This announcement is published on/at/in http://bla.bla.com".

When we refer to the "website" itself, what preposition should we use? Such as in: "You can also find this information on/in/at this website."

Thanks for your help.

Examples:

One can find information about learning English at www.antimoon.com.

I post on a forum on the Antimoon web site.

Can I conclude as follows:
1. We use "at" before a name of a website, such as http://www.antimoon.com.
2. We use "on" before a more general reference name, such as "on the Antimoon web site".

Is it correct?

So that, when I want to refer to a website, it should be like this:

1. "This information was first published on Microsoft website."
2. "The more information about the latest virus update can be found at the following website http://www.microsoft.com."