1. Securing online social networks against bad bots based on a necklace captcha approach;Torky,2016
2. Search prevention with captcha against web indexing: A proof of concept;Kim,2019
3. Tell me about yourself: The malicious captcha attack;Gelernter,2016
4. Research on deep learning techniques in breaking text-based captchas and designing image-based captcha;Tang;IEEE Transactions on Information Forensics and Security (TIFS),2018
5. Hitting three birds with one system: A voice-based captcha for the modern user;Shah,2018