By Ian Bush

PHILADELPHIA (CBS) – A hacker group claims it has millions of user IDs for iPhones and iPads — along with names, cell phone numbers, and mailing addresses that go with them. But it’s also troubling to learn from where all those details were stolen.

The FBI disputes this, but hackers who call themselves AntiSec say they plucked all this information from the laptop of an FBI supervisor special agent. But why were these details on that computer in the first place?

“I’ve talked to many of the people whose information was released. They’re dumbfounded.”

CNET senior writer Greg Sandoval says Antisec doesn’t have credit card numbers, but this information is highly personal — it ties someone to his device and home, and can give password hints.

“It’s very dangerous.”

One million users have had their information splashed online — but 11 million more people are affected.

“This hacker group says they don’t have any malevolent wishes for this information, but just putting it out there has enabled people to come and get it anytime they want.”

TheNextWeb has published a tool which lets you check your Apple device’s UDID: www.thenextweb.com.

But remember, there are millions more devices that have been compromised but not published by these hackers.

If you don’t have an app that tells you your UDID, plug your device into a computer. Open iTunes, select the device, and click the serial number to reveal the UDID.