However, if not carefully designed, electronic polling systems can be easily compromised, corrupting results or violating voters' privacy. Many designs exist for electronic polling systems that are secure and private, but impractical for large-scale elections. It is not possible for a vote to be altered, a validated vote to be eliminated from the final tally, or an invalid vote to be counted in the final tally. Only eligible voters can vote, and each eligible voter can vote only once. Nobody can link any ballot to the voter who cast it, and no voter can prove that he or she voted in a particular way.
Voters can independently verify that their votes have been counted correctly.
Voters can cast their votes quickly, in one session, and with minimal equipment or special skills. A variety of ballot question formats including open ended questions are permitted. There are no restrictions on the location from which a voter can cast a vote. However the more private of these schemes are inconvenient or impractical for large-scale elections. Voters use the tags as tokens that permit their votes to be counted.