Poll cookies

Great Poll script.
However, am I right that when someone has voted, then delete his browser cookies, he can vote again?
If so, any way to prevent that?

Thanks

No reactions?
OK.
What I meant to say is that instead of using cookies, maybe it would be a better idea to use some ip-blocking script once someone has voted. In my opinion this results in a lesser chance on cheating.
Maybe a suggestion for a later version?

However, I began writing myself and succeeded in creating a script that logs ip-addres, places it in an array and blocks it the next time.
However, I get stucked because the script only seems to recognise the last added ip-addres.
If someone wants to help me out, I would gladly post (or send) the script.