11. A CAPTCHA system comprising: a database configured to provide information comprising an advertisement word; and a CAPTCHA processing unit comprising a processor configured to receive a CAPTCHA request comprising category information of an application service from an application server; respond to the application server with a token identifying the CAPTCHA request and a CAPTCHA image comprising a distorted advertisement word associated to the category information and a series of randomly generated and distorted characters, both the advertisement word and the characters being a CAPTCHA text intended to be typed by a user via a user equipment connected to the application server; receive from the application server the token and a CAPTCHA answer submitted from the user equipment by the user; and verify the token and the answer and return to the application server a result of the verification.
11. A CAPTCHA system comprising: a database configured to provide information comprising an advertisement word; and a CAPTCHA processing unit comprising a processor configured to receive a CAPTCHA request comprising category information of an application service from an application server; respond to the application server with a token identifying the CAPTCHA request and a CAPTCHA image comprising a distorted advertisement word associated to the category information and a series of randomly generated and distorted characters, both the advertisement word and the characters being a CAPTCHA text intended to be typed by a user via a user equipment connected to the application server; receive from the application server the token and a CAPTCHA answer submitted from the user equipment by the user; and verify the token and the answer and return to the application server a result of the verification. 16. The CAPTCHA system according to claim 11 , wherein the CAPTCHA processing unit is further configured to allow the Application publisher to add or delete a license for using CAPTCHA for each application service and the corresponding category information of the application service; and to allow the advertiser to add or delete the advertisement word and the corresponding category information of the advertisement word.