Your UDID is showing.
Last week we learned about a study that found that two-thirds of Android's top applications handled user data in a suspicious manner. Now another study has found that iPhone users are also at risk of being tracked through app use.
Bucknell University Assistant Director of Information Security and Networking Eric Smith conducted a study and published the paper "iPhone Applications & Privacy Issues: An Analysis of Application Transmission of iPhone Unique Device Identifiers (UDIDs)." In it, his team looked at 57 of the top free applications from the iTunes App Store and found that 68 percent of apps transmitted the UDID.
The UDID of the iOS device itself isn't sensitive, but sometimes that UDID would be paired up with your real user information that the app has been granted access to.
"For example, Amazon’s application communicates the logged-in user’s real name in plain text, along with the UDID, permitting both Amazon.com and network eavesdroppers to easily match a phone’s UDID with the name of the phone’s owner. The CBS News application transmits both the UDID and the iPhone device’s user-assigned name, which frequently contains the owner’s real name."
One of the chief concerns is that what these corporations could potentially do with this linked data, such as selling it to those using it for more nefarious, annoying and invasive marketing tactics.
(Source: Ars Technica.)

For you iPhone fanboys, 68% is greater than two-thirds; which means iPhone are MORE insecure than Android phones. So... you guys can get off your high horse now.
who are you talking to? Please be specific. scream at a wall much?
For example if Symbian or Blackberry or Windows Phone apps all do the same thing then we can just chalk it down to a problem inherant with smartphones.
However.
If it turns out that one or more of the others are "clean" then buyer beware, vote with your feet and purchase a smartphone that doesn't spy on you.
Or at least not download free apps that just imitate the existing mobile web page.
android app store is open and dirty, like some kind of black market, you have to hunt and gamble for the good ones. apple app store is closed and limiting, is there no middle ground? just accept all apps as long, for example, as they don't send your GPS data directly to a mysterious server?
There is a middle ground
Go to www.download.com
I like the black market, basically the whole internet is a free app black market for 1337 people. The threats are the same. So if your are too dumb to know whats what, buy an apple product!