What type of plug-in is used on those "type the letters you see in the box" with all those distorted letters? Used on websites such as myspace... to prevent bots from spamming I guess. Thanks.

It's called "captcha" or something along those lines. google it.

Yeah it's called a captcha.

If you are looking to use one on your website, I recommend using recaptcha (http://recaptcha.net/), which even craigslist uses.

Or you know, you could make your own. I use a simple common knowledge captcha that I made in PHP.