Usually I can get these little "captcha" security things on the first or second try.  Here's the one Facebook greeted me with yesterday.  Any idea what the string of letters is supposed to be?  The audio captcha was just as worthless.  My solution?  After about 7 or 8 tries, I went and used a different computer that was already logged into Facebook.  In fact, I still haven't gotten onto FB using that other computer.

It's like the wall surrounding the chocolate factory in "Willy Wonka":  "Nobody gets in...and nobody comes out."  At least it's secure!