SAN FRANCISCO (AP) — Apple has booted a developer and his apps from its applications store after hundreds of hijacked user accounts were used to push his titles to best sellers over the weekend.

Developer Thuat Nguyen has been banned for violating an Apple license agreement, “including fraudulent purchases,” Apple spokeswoman Trudy Muller said Tuesday. About 400 iTunes users were affected, she said.

Technology blogs said some iTunes users unwittingly had their accounts used to buy Nguyen’s book apps, which at one point occupied 42 of the top 50 book apps sold in the store.

“A vast majority of these book apps were released in April, have little to no customer ratings or reviews, appear to be in Vietnamese … and may or may not be infringing on copyrighted work — we’re noticing a lot of Dragon Ball art here,” the blog Engadget.com said on Sunday.

Apple’s app store offers paid and free applications for the iPhone, iPad and iPod Touch.

Muller said iTunes’ servers, which hold credit card information for iTunes’ 150 million users, were not compromised.

Security on iTunes is being bolstered by requiring users to enter their credit card’s security code more often when making purchases or entering the site from a new computer, she said. She noted that developers do not get any confidential iTunes customer data when an app is downloaded.