One Time Password (OTP) is used for Web Application login to validate user. OTP's are of two types 1.Email 2.Mobile. Mobile SMS is used when there are plenty of users. Email is used when there are business users. For business users when he/she enters userid and password email is generated from the same email server. So no chance of mail delivery delay. OTP is valid for specific time period, it invalidates either upon use or period expiry. So security is maintained.
1. Maharashtra https://www.maharashtra.gov.in 2. Uttar Pradesh http://up.gov.in 3. Karnataka http://www.karnataka.gov.in/english/pages/home.aspx 4. Tamilnadu http://www.tn.gov.in/