The company said the hack occurred on Thursday 18 July and could have resulted in developers’ names and email addresses being compromised. However, Apple insists sensitive personal information was encrypted and could not be accessed.
Apple took the developers' site down on Thursday after detecting the attack and left a "we’ll be back soon…this site is undergoing maintenance for an extended period today" message, before informing developers of the attack yesterday.
Apple claims it is completely overhauling its developer systems, updating its server software and rebuilding its "entire database" in order to prevent a similar security threat.
The hack comes as other tech firms struggle to prevent hacks into their systems, with Sony Computer Entertainment being fined £250,000 on its PlayStation Network that compromised the personal details of millions of its users.
The European Commission is in the process of pushing through cyber security legislation that could force companies to reveal any major hacks into their systems, as it seeks to improve consumer trust in the digital economy.
Legislation would enable governments to name and shame companies that have not done enough to put measures in place to protect their data.