1. Send Group Message: send the same instant message to all contacts in a certain group.
Go to contacts list, and right click a certain group to select "Send Group Message". The Send Group Message window opens.

In the Group window, type your message, then click the "Send" button. When you click the "Send" button, each contact receives your message.

Or click "Select Contacts" and select contacts at the pop up window beside the conversation window. Then click "Add selected contacts".

2. Messaging selected contacts: send an instant message to all selected contacts.
When making multiple selections, Ctrl-click to select randomly. Rest "Ctrl", right click one of the selected contacts and select "Send IM". The Send Message to selected contacts window opens. Type your message, then click the "Send" button".

Note: only when your activity is over level 9, could you messaging multiple contacts.