Block A Contact

When you are involved in an instant message with someone you want to block, click Block on the toolbar. (If other people are in the conversation, click Block, and then click the name of the person you want to block.)

–or–

In the main window, right-click the name of the person you want to block, and click Block. In these cases, you are essentially moving someone from your Allow list to your Block list. To see those lists or move people between them, click the Privacy tab in the Options dialog box (Tools, Options).