One of the world’s largest telecoms and IT services companies has revealed that attackers may have stolen data from its internal systems, affecting over 600 customers. NTT Communications provides cloud, network and data center services to some of the world’s biggest companies. Its parent, NTT Group, is ranked in the top 100 of the Fortune Global 500. The firm claimed in a lengthy statement on Thursday that it detected unauthorized access to its Active Directory (AD) server on May 7, confirming the attack four days later. Although an English language version of the notice has yet to be published, it appears that hackers first compromised a cloud server (labelled server B by the firm) located in its Singapore data center, before using it as a stepping stone to attack another internal server (server A) and its AD server.