AT&T admitted today a security weak spot that exposed the email addresses of apparently more than 100,000 users of Apple's iPad to precision-targeted hacking attacks.
The vulnerability affected only iPad users who signed up for AT&T's 3G wireless internet service.
It involved an insecure way that AT&T's website would prompt iPad users when they tried to log into their AT&T accounts through the devices.
The site would supply users' email addresses to make log-ins easier, based on unique codes contained in the SIM cards inside their iPads. SIM cards are used to tell mobile phone networks which subscriber is trying to use the service.
The hacker group that claims to have discovered the weakness - the group calls itself Goatse Security - said it was able to trick AT&T's site into coughing up more than 114,000 email addresses, including those apparently of famous media personalities and important government officials.
A representative for the group said today the group contacted AT&T and waited until the vulnerability was fixed before going public with the information.
AT&T said the problem was fixed on Tuesday but that it was alerted to it by a business customer.
Gawker Media's Valleywag website earlier reported on the breach.
AT&T said it would notify all iPad users whose email addresses may have been accessed.
"We take customer privacy very seriously and while we have fixed this problem, we apologise to our customers who were impacted," the company said.
AT&T noted that the only information hackers would have been able to steal using this attack were users' email addresses.
But that can be enough to launch a highly effective attack, since the attacker also knows that the person receiving the email is an iPad user and an AT&T customer and would expect to receive e-mail from Apple and AT&T about their accounts.
Criminals could use that knowledge to trick them into opening emails that plant malicious software on their computers.
An Apple representative deferred requests for comment to AT&T.
Apple has sold more than two million iPads since they went on sale two months ago.
The iPad comes in two different set-ups - one that only connects to the internet via wi-fi, and another that also can connect through AT&T's 3G network. The wi-fi-only models are not affected by the breach.