Apple has begun using secure Web pages -- HTTPS -- for all App Store communications. The move mitigated a number of vulnerabilities that attackers could have exploited to steal App Store passwords, force users to pay for unwanted apps or intercept user data.

Apple announced the security change earlier this year, noting that "active content is now served over HTTPS by default" for App Store via its iTunes applications. Apple's security notice credited multiple researchers for alerting it to the vulnerability, including Google researcher Elie Bursztein.

Bursztein said Friday in a blog post that Apple's previous failure to use HTTPS for App Store communications -- except on purchase pages – along with its failure to confirm certain activities and the dynamic manner in which App Store pages get generated left users open to "an active network attack that is able to read, intercept and manipulate non-encrypted (HTTP) network traffic," for example, via unencrypted public Wi-Fi hotspots.

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"Being on the same networks as the victims is all it takes [to facilitate man-in-the-middle (MITM) attacks]," he said.

For example, an attacker could have stolen passwords by inserting a fake password-notification prompt into the App Store application update mechanism and swapping a paid app for a free app that a user tried to obtain, thus charging them. Users could also have been tricked into paying for fake app upgrades and been blocked from installing an app either by hiding it from view in the App Store or tricking the user into thinking it was already installed. Finally, Bursztein said the vulnerabilities posed a privacy-leak problem, because "the App Store application update mechanism discloses in the clear the list of the applications installed on the device."

Apple's adoption of HTTPS for all App Store communications follows -- and arguably lags -- similar moves made by Google, which began exploring the use of HTTPS for encrypted search in 2010 and made it the default for all communications with Google services, including Gmail, in 2011. Similarly, Facebook adopted HTTPS by default late last year, as did Twitter.

Last year, Mozilla announced that Firefox would default to the HTTPS version of any website, taking a cue from the HTTPS Everywhere campaign and related plug-in advanced by Electronic Frontier Foundation, which seeks to get more sites to adopt the security offered by HTTPS pages.

Calls for websites to adopt HTTPS increased in the wake of Firesheep, a Firefox plug-in that was released in late 2010 that focused attention on the ease with which traffic being sent across unsecured hotspots -- for example, in many cafes and airports -- could be intercepted. The fix for such attacks was easy: websites needed to enable HTTPS by default, thus adding an encryption layer to all HTTP communications between browser and website.

"Apple, it seems, didn't bother with HTTPS Everywhere, even for its own App Store, until 2013," said Paul Ducklin, head of technology for Sophos in the Asia Pacific region, in a blog post. "Since there's no other place to shop when you're buying or selling iDevice software, and since Apple likes it that way, you might think that Cupertino would have set the bar a bit higher."

How long has Apple's use of HTTP for its App Store put users at risk of being exploited? "I am unsure," Google researcher Bursztein said via Twitter. "I reported it in July [2012], but likely they have been susceptible to MITM for years."

But Bursztein hopes that Apple's adoption of HTTPS for its App Store will lead more developers -- "in particular mobile ones" -- to likewise adopt HTTPS. "Enabling HTTPS and ensuring certificates validity is the most important thing you can do to secure your app communication."

"Please don't let your users down," he said. "Do the right thing: use HTTPS."

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