With tremendous increase of number of users on internet. Online security has become a very important issue. Whether it is information related to an organization or an individual, if stolen it can lead to serious financial loses. The typical validation method used on the Internet is single-factor authentication, where users supply a username and password. This approach has significant drawbacks, particularly as cyber criminals become more organized and adept. Thus idea of using Multi-Factor Authentication has been introduced in the world of internet to harden the security of network and make it difficult for the attackers to crack systems. In this mechanism, users are required to provide some extra information along with their login Id and password. Most popular is using One-Time Passwords that are generated randomly and valid only for single login and even for short duration of time. In this paper review of various login authentication techniques has been performed, discussing pros/cons and attacks through which security of each can be compromised.