If the objective is to restrict blogging activity, network-monitoring software probably isn't the most efficient way to do so. I'd recommend implementing a content-filtering product, such as Secure Computing Corp.'s Webwasher SME250 or Websense Inc.'s Hosted Web Security tool. These products come with built-in Web categorization databases that help monitor certain types of unwanted traffic, such as blogging sites, pornography, etc.
If you choose to implement content filtering, a word of warning: no filtering scheme is perfect, and it's difficult to defeat someone who is determined to bypass such filtering. For example, if you allow users to access secure websites using HTTPS, it won't be possible to inspect the contents of their encrypted traffic. Bypassers could set up an encrypted proxy at home and use it to route traffic elsewhere on the Internet. Also, while content filtering databases may contain well-known blogging sites, such as Blogger and Wordpress, they can't possibly track all of the little-known single blog sites out there on the Internet. You can build a wall if you like, but it's going to be made of Swiss cheese.
This was first published in December 2008