Polls: Students can click on every option & 'Hack' polls

We just discovered that when a student (or teacher) makes a poll, that the other students can choose every option and then vote. Also - several of my students figured out that they can 'hack' a poll and vote multiple times. What they were doing was voting once, then clicking on the X above the poll and then, instead of the graph showing up with the current poll results, they were given the option to vote again on the same poll. the were using this backdoor to hack several of the polls other students made. Other students said they could hack the polls by voting and then, once the bar graph comes up, they click on the poll question again (in the middle column of the screen) and then the voting choices come up again. Thanks!
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