Is there a way to block all Facebook users, for example who work in X, and I don't want them to find me in search or even see my user account?

I know you can make it so that no one can find you in a search and that you can block individual people, but I don’t think you can block a whole group (of people that aren’t your friends). You can block people that are already your friends and in a specific group from certain information though. To do that, go to privacy settings, then go to customize settings under sharing on facebook. Then you can select customize (in the drop down box) for each area and block the specific groups (as in the groups that you put your friends into) by typing the group name in the box that says to block from these people (or something like that). If they aren’t your friend, I think you would have to block each person individually.

you can block people in a certain group if and only if you are also in that group. However, that will not necessarily block everyone that you wanted to. For example, if you wanted to make sure that no one who works at Acme could see you, you could join the Acme employees’ group, and set your privacy settings to hide your posts/statuses/etc from the Acme employees’ group. However, you have no guarantee that everyone who works at Acme has actually joined the Acme employees’ group.

The only way to be sure is to block EVERYONE by default, and only allow people you’ve actually friended to see you. Go into your Privacy settings, and change your visibility to only friends. This means your friends who are not yet your Facebook Friends will not be able to see you either – you’ll have to add them, they won’t be able to search for you.

@MrItty I have my settings like that, but people still find me and “friend” me. Are they finding me through people who are already my “friends”?

I suggest checking your settings again.
Account->Privacy Settings->Basic Directory Information->View Settings->Search For Me on Facebook. Change that setting to “Friends Only”

BTW – I found that the Customize Settings give me the most powerfull tool in Facebook. So far it was fine. I do have my friends in groups so I can set which group will see what or block a group from seeing something, but this is only for My Friends in my account.