There are many websites on internet who says they will give more and more upvote on your posts. They want to sing in your steemit account on their website. They are totally fraud.. They want to steal your steemit account.
Sometimes they want to take your steem dollars to give you more and more upovte. They are scammers. They will receive your dollars but they won't give you any upvote.
Be careful. Don't do that. First check everything.