Apple has prohibited a developer from its App Store after it was found that the developer was involved in fraudulent purchases of his applications from around 400 accounts, it said in a statement.

Thuat Nguyen and his apps, which at one point over the weekend supposedly occupied 42 of the top 50 positions in the book sales chart, was taken out of from the App Store for breaching the developer Program License Agreement, Apple's Trudy Muller said by e-mail.

The iTunes servers were not compromised, said Muller, adding Nguyen did not get any confidential information when his apps were downloaded.

Apple recommended users, who made notice of the fraudulent purchases, to contact their bank and cancel the credit card that came under scrutiny. Apple also advises users to bring changes in their passwords.

Due to the occurrence of this instance, Apple is tightening security on App Store purchases and users will be able to see that more number of times they will need to submit the CCV number on their credit cards.

The CCV (card code verification) code is characteristically a three-digit number that is printed on the back of the card, which is not a part of the credit card number and isn't stored by Apple's servers.