The developers said they noticed dozens of applications by the same author surge into the top rankings, although the applications frequently had few or no user reviews and appeared to be roughly coded.
The incident coincided with reports that iTunes Store users were charged for applications they say they did not purchase, suggesting that their accounts may have been compromised.
Romanian developer Alexandru Brie wrote on his blog that his "Self Help Classics" application had been bumped from the top 50 paid book applications in the U.S. The application had been in the top 20 for the last 18 months, Brie wrote.
Of the top 50 book applications, about 41 were roughly coded applications that appeared to be Vietnamese but were not localized, Brie wrote. Many of the applications were similar and had no user reviews despite being listed as top paid ones, he said.
Brie's application sold at a slower pace as a result of being pushed out of the top 50, he said.
"I had hoped things would get back to normal thinking that, eventually, these weird apps would just go out of fashion," Brie said in an interview. "There was a drop in sales, not only for me but for all the developers whose apps had been shifted by the 41 apps in question."
Brie wrote that he was contacted by another iPhone app creator who had noticed the apparent anomaly, QuickReader developer Patrick Thomson.
"It looks like the Books category has been hijacked by an app publisher named mycompany/Thuat Nguyen," Thomson wrote in an e-mail to Brie. "His apps now occupy 40 of the top 50 ranks in the Books category on the app store. These are apps that typically wouldn't rank in the Books category and most of them don't have any ratings or reviews."
The issue may have been a problem for Apple for more than two weeks. As far back as June 14, several applications from mycompany were listed as top-grossing ones in the U.S. at App Annie, a company that tracks iPhone applications.
At least one of the 40 or so similar applications had comments from reviewers saying their account had been hacked and used to purchase the application, Thomson wrote.
"It would appear that this publisher is hacking accounts and buying his own apps in order to drive up his rankings in the Books category," Thomson wrote. "This is having a negative impact on our apps, which are being pushed down in the rankings and losing visibility, plus it makes for a bad user experience."
As of Monday, Brie said his application had returned to the top 10 paid ones for books in the U.S. The mystery applications -- captured in a screen shot on Brie's blog -- also have been removed.
Brie said in an interview, however, that there are a couple of other similar-looking suspicious applications in the top 200. "I noticed these ones haven't been removed as of yet," Brie said. "Perhaps Apple is investigating them in more detail, as they are not as obvious as the first ones.
Apple officials contacted in London did not have an immediate comment.
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