

Facebook Knows When You Open Their Emails. How? Creepy Silent Sounds… - mirceagoia
http://pandodaily.com/2012/03/06/facebook-knows-when-you-open-their-emails-how-creepy-silent-sounds/

======
mirceagoia
Excerpt from the article:

A friend-of-a-friend tipped us off over the weekend to a rather clever way
that Facebook is taking it one step further: non-existent sound files.

You can see it yourself by opening just about any email sent by Facebook in
the past year or so (and possibly even earlier) and looking at its raw HTML.
Somewhere in there will be a bit of code that looks like this:

<img
src=”[http://www.facebook.com/email_open_log_pic.php?mid=XXXXXXXXX...](http://www.facebook.com/email_open_log_pic.php?mid=XXXXXXXXXXXXXXXXXXXXXXXXXXXX”)
style=”border:0;width:1px;height:1px;” />

<bgsound
src=”[http://www.facebook.com/email_open_log_pic.php?mid=XXXXXXXXX...](http://www.facebook.com/email_open_log_pic.php?mid=XXXXXXXXXXXXXXXXXXXXXXXXXXXX”)
volume=”-10000″/>

The first bit, the img source line, is Facebook’s tracking pixel. It tells the
mail client to ping Facebook’s server for an image that doesn’t seem to
actually exist. Facebook’s server sees the request, and can use the email’s
unique 28-character identifier, shown above as a series of X’s, to flag that
email as having been opened.

