Ask NH: Are people hacking hacker news?

In recent days, I have seen a lot of stories/urls/questions, which do not deserve to be on first page of HN, but they are.

It is obvious that the story will gradually move down the list if its content has no worth, but to be on first page gives enough exposure.

If I ask some of my friends to vote my submission up within minutes of submission, it will bring the story on first page and then if I ask them to keep voting in batches, the story will stay there.

I am not sure whether HN algorithm checks for such voting patterns or not. If it does not, how can it or we prevent such acts?