How can I 'hide' that I am on facebook so that friends don't see my profile picture telling them I am currently on line?

[hmc]

One friend in particular has too much time on his hands and seems to want to engage in those IM type chats when I've only just popped on for 2 minutes to check what's going on......I feel guilty ignoring him and it would be so much easier if he didn't know I was online

Click the chat box in corner ,click options then click go offline.

Brilliant - thanks!