See also this newly created a Bug Report.
There is an on-going discussion on how to fix this issue with the steem Devs: https://github.com/steemit/steem/issues/233

> Both Hot and the Vote Count can be easily manipulated to make an article more visible and thus indirectly increase payout.
Using the API we can easily create hundred of accounts whenever a POW is found. In fact this behaviour is encouraged in order to mine continuously, or we are penalized. However when duplicate accounts are used to upvote content than it skyrockets in the Hot section. Also the vote count is misleading as it suggest that many low steem power users support the post although it is actually the same person.
The below image is a an example. It was upvoted with 150 Bot accounts and appears at the top of the Hot section although there is little payout associated with it.
![](https://i.imgsafe.org/fba2b190fe.png)