Apple has banned a Vietnam-based developer from its online applications store for manipulating sales figures to boost his ranking.
The company removed Thuat Nguyen for violating Apple's developer program licence agreement, according to US reports.
According to Apple, the iTunes servers were not compromised and Nguyen did not get any confidential information when his apps were downloaded.
Apple has not revealed how Nguyen manipulated the data, sparking speculation that he hacked into user accounts to make unauthorised purchases.
The company insists that neither App Store nor iTunes users' information is at risk as a result of Nguyen's activities.
But Apple has cautioned its customers to be vigilant for suspicious transactions and recommended that they change account passwords immediately and cancel credit cards if they suspect fraudulent purchases were made.
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The company is also tightening security on App Store purchases, such as increasing the number of times users are asked to enter the card verification number.
Apple's App Store, Google's YouTube and Wikipedia were among several top sites to be disrupted on US Independence Day, but no definite connections have been established between them.