In an email to users, ComiXology revealed that an "unauthorized individual" accessed a database containing usernames, email addresses, and cryptographically protected passwords. Payment information associated with accounts is not stored on the company's servers, and thus was not included with the data obtained in the breach.
Though the passwords stolen were encrypted, ComiXology is nevertheless requiring users to change their passwords as a precautionary measure. The company has also recommended that users change their password on any other website where they may use the same or a similar password.
ComiXology apologized to users, and said that it has taken on measures to strengthen its security going forward.
Purchases through ComiXology's iOS applications are controlled by Apple through an iTunes account, but the company's cloud-based platform allows digital titles to be synced with other applications and viewed on other devices through a separate ComiXology account.
Offering digital comics from both Marvel and DC, the two biggest comic publishing firms, ComiXology is the largest cloud-based comic seller. For years it has been the top-grossing non-game application available on the iPad.
In addition, ComiXology also powers digital comic sales for official Marvel and DC applications on iOS, both of which also frequently appear among the top grossing options on the iPad App Store. As of Thursday morning, ComiXology ranks No. 10, the Marvel Comics app is No. 38, and the DC Comics app is No. 41.