Type [100:0] then submit, in any textbox in Facebook

I think it would be helpful if you posted what this actually does. A short description or a screenshot would be great.

I, and I assume a lot of the HN crowd, am not all that keen on randomly entering things when we have no idea what it does. I know it looks, and most probably is, harmless, however who knows what silly vulnerabilities a little bit of apparently harmless code might do to such a complex system as Facebook.

This is a very cool trick in Facebook :) If you put @[[userid]], it will be replaced with the profile pic of that userid! Now that people know this, there are a bunch of profiles which only exist to be convenient as emoticons. http://www.digitspark.com/2011/12/how-to-use-anyones-face-as...

I'm getting a request from $100,000 Pyramid to access my account?

Posting @[100:0] results in the following:

Andy Brunner

You're right, which is weird (I don't know who he is). When my friend showed me, it's replaced with "Mark Zuckerberg".

@[2:0] results in a link to a Birthday Calender app?

I'm getting peoples names instead of pictures.

Try one bracket vs. double brackets?