This errata is from the D&D Rules Compendium; I expect it’ll be put in the official errata document when that is next posted. Note that you can’t become hidden in “Concealment” – sorry, Nate!

STEALTH
Armor Check Penalty
Make a Stealth check to conceal yourself from enemies, slink past guards, slip away without being noticed, and sneak up on people without being seen or heard.

This skill is used against another creature’s Perception check or against a DC set by the DM.

STEALTH
Stealth: At the end of a move action.

    Opposed Check: Stealth vs. passive Perception. If multiple enemies are present, your Stealth check is opposed by each enemy’s passive Perception check. If you move more than 2 squares during the move action, you take a –5 penalty to the Stealth check. If you run, the penalty is –10.

    Becoming Hidden: You can make a Stealth check against an enemy only if you have superior cover or total concealment against the enemy or if you’re outside the enemy’s line of sight. Outside combat, the DM can allow you to make a Stealth check against a distracted enemy, even if you don’t have superior cover or total concealment and aren’t outside the enemy’s line of sight. The distracted enemy might be focused on something in a different direction, allowing you to sneak up.

    Success: You are hidden, which means you are silent and invisible to the enemy.

    Failure: You can try again at the end of another move action.

    Remaining Hidden: You remain hidden as long as you meet these requirements.

Keep Out of Sight: If you no longer have any cover or concealment against an enemy, you don’t remain hidden from that enemy. You don’t need superior cover, total concealment, or to stay outside line of sight, but you do need some degree of cover or concealment to remain hidden. You can’t use another creature as cover to remain hidden.

Keep Quiet: If you speak louder than a whisper or otherwise draw attention to yourself, you don’t remain hidden from any enemy that can hear you.

Keep Still: If you move more than 2 squares during an action, you must make a new Stealth check with a –5 penalty. If you run, the penalty is –10. If any enemy’s passive Perception check beats your check result, you don’t remain hidden from that enemy.

Don’t Attack: If you attack, you don’t remain hidden.

    Not Remaining Hidden: If you take an action that causes you not to remain hidden, you retain the benefits of being hidden until you resolve the action. You can’t become hidden again as part of that same action.

    Enemy Activity: An enemy can try to find you on its turn. If an enemy makes an active Perception check and beats your Stealth check result (don’t make a new check), you don’t remain hidden from that enemy. Also, if an enemy tries to enter your space, you don’t remain hidden from that enemy.