@inproceedings{CHI-2011-FidasVA,
	author        = "Christos Fidas and Artemios G. Voyiatzis and Nikolaos M. Avouris",
	booktitle     = "{Proceedings of the 29th ACM SIGCHI Conference on Human Factors in Computing Systems}",
	doi           = "10.1145/1978942.1979325",
	isbn          = "978-1-4503-0228-9",
	pages         = "2623--2626",
	publisher     = "{ACM}",
	title         = "{On the necessity of user-friendly CAPTCHA}",
	year          = 2011,
}