ASP.NET preventing a user from successive logins
<p>I'm working on a web-based academical evaluation project (VS2010,C#,ASP.NET). Users can enter the web site and evaluate personnel of a company (or the company managers). Then my clients (company owners) should be able to view results of the evaluation (appraisal). As this process involves people and there is always risk of re-voting by some users, I'm searching for ways to minimize number of re-evaluations by similar users, i.e. I'm going to prevent a user from voting for more than once as it can hugely affect results of the appraisal process, I'm asking user about his name, surname and national ID; I'll store these data in my database, and the next time a user trying to login with the same data will get a warning, but anyone can change his data and vote for several times! Also I save user IP and will check it on later logins but it can also be faked easily! what else can I do? using cookies? sessions? how should I technically prevent users can from voting for several times?</p>

<p>thanks</p>
