How information leaks on Facebook: a semi-private URL vs. Picasa web albums

This is mundane, but worth noting.

For years we kept some shared family material private by not sharing the URL. It worked, the site was never indexed -- until recently.

I'd shared one of the album URLs on Facebook. That did it. Even though my page contents are shared only with friends, I suspect Facebook indexes any URLs it comes across. Probably most of my friend's Pages are not themselves public, so their view of my post was probably shared.

It's not a surprise that the URL leaked, but it's noteworthy that it remained private through tend years of Google. It only broke when I started using Facebook.

I renamed the URL, so it's secret again. I won't publish the new URL to Facebook, I'll return to sharing by email.

So what about Picasa Web Albums? They are also commonly shared by exchanging a "secret" URL, and I've shared some on Facebook. Interestingly these aren't indexed in Google, perhaps because Google doesn't index non-shared albums.