On February 12, Frederic Lardinois wrote on ReadWriteWeb:
Over the last few days, there has been a lot of buzz about how much private information your public Google profile contains if you don’t choose the right settings. The URL of your profile alone can already give away your Gmail address. To hide this address from public view, you can switch your profile URL away from showing your name to using an address that features a 21-digit number instead of your username. However, as it turns out, this isn’t a foolproof method either. By using a very simple trick, anybody can quickly figure out your Gmail address from these numbers.
Security blogger The Harmony Guy just told us about how this hack works. While the way to reveal these addresses isn’t obvious, you can easily follow along and try this method out yourself…..
As it turns out, that trick no longer works, as Google subsequently adjusted their services. But as The Harmony Guy notes:
Still, it’s wise to be cautious when using a tool that interacts with so many other services.
It’s also wise to wait before enabling or signing up for new services. It seems that every announcement of a new service or change in default settings is followed shortly thereafter by an announcement of privacy concerns about the service.