Captcha: Facebook Fight For Social Spammer

Ever wonder why browsing Facebook are more peaceful now? No person message you or post in your wall with "Christian I cant believe it, I actually got..... (some nonsense message)" that cause some user to be angry and said some said foul language (I don't blame them instead I respect them). The reason is, Facebook now extends its security by the use of captcha (program that can generate word that humans can answer but computers cannot). 

Lately I thought Facebook have no intention to act for social spammer and the only simple action I observe is the the number of URL that can share is limited per day (25 (estimate for same link shared)) but wrong. While social spammer continuously spreading spam message (I think by the use of some script that causing Facebook to become slower than before), Facebook built a number of automated system to detect spam and potential spam and block those responsible. When Facebook find a URL that they know is spam, Facebook add it to a blacklist and prevent it from being sent or posted (I think the picture below is the message if the URL posted is in the blacklist). 


Facebook also knows that spammer are smart and also concern for me and other user as well so they created a greylist for URLs that might be spam, but might also be legitimate. Captcha will only be activated when users try to send or post a greylist which required to solve in able to post a greylisted URL (picture below is a sample of captcha when user try to post a greylisted URL).