A Free CAPTCHA Control for ASP.NET 2.0 on CodeProject:
“CAPTCHA is short for "completely automated public Turing test to tell computers and humans apart" and is the most popular technique used to prevent computer programs from sending request to Web servers. This can for meta-searching search engines, doing dictionary attacks in login pages or sending spam using mail servers. You may see CAPTCHA images in Google register page when you do availability check on too many usernames or in Yahoo, PayPal and many other big Web sites.“
Learn more here.
If you are having problems with Comment SPAM on your blog or websites, don't forget to checkout ReverseDOS:
“ReverseDOS is a very simple HttpModule that checks various parts of incoming requests against a list of crap that you don't want pushed on to your site. If ReverseDOS detects a match, it attempts to stall the requesting client for a number of seconds (specified in a .config file). During this loop, which uses virtually no server resources - and only a tiny smidgen of bandwidth, ReverseDOS checks every .3 seconds to see if the client is still connected. If the spammer disconnects, good riddance. If the spammer sticks around, they're finally rewarded with the Response Headers - containing an HTTP 403 - Access Denied Response Code. (Awwwhh tooo bad...)”
More Must Have .NET Developer Tools.
Source: David Hayden ( Florida .NET Developer )