activation code in asp.net?

when a user asks for forgot password , i send an activation email which wor开发者_JAVA百科ks okay. but when the user activated the code and created the new password, if the user try to access the activation code for second it should say the activation code is failed/Invalid. how to check the clicks on the activation code?

You could delete the activation code from your database, once it has been used successfully? (or generate a new one "for next time")

Have a flag in the database that marks it as invalid.