| Overview | Making Yourself Invisible | Changing Your Stealth Setting | Ignoring a Contact |
Yahoo! Messenger strives to provide an environment in which you feel safe, while letting you enjoy easy access to your contacts. Messenger offers a number of ways to avoid interactions with people you don’t wish to communicate with while using the Messenger features, including:
Invisibility—Shows you as unavailable to every contact who has your name on their Messenger List. You can decide to be invisible when you sign in, or set the invisible state while using Messenger.
Stealth setting—Lets you to
appear online to some people and offline to others. You can activate a stealth setting
for an entire group or
for individuals. Not available with Facebook friends or Pingbox™ visitors. 
Ignore—Shows you as unavailable to specified contacts
and stops all communication from them. These contacts can initiate
communication from their computers, but you won’t see or hear any
attempts to contact you. This is the right choice to make when you
really don’t want to interact with someone. To use this feature,
the contact’s name can’t be on your Messenger List. You can ignore
contacts on your Ignore List or
anyone who isn’t on your Messenger List. Not available with Facebook
friends or Pingbox visitors. 
You can change your status to offline for all contacts who have your name on their Messenger Lists by signing in as invisible.
For a general guide to internet safety, take a look at the Yahoo! Safely site.