With fast development of cloud computing, more and more sensitive data are stored in distributed storage systems. It is mainly suffered from the following two threats: (i) data at rest are stolen; and (ii) data in transmission are intercepted. The threats may lead to serious problems. For example, personal private data eavesdropping may lead to legal problems and credit crisis, while company information leaking may cause huge economic loss. To tackle such security threat in cloud distributed storage system, we propose a novel scheme to produce dynamic size of shares with multiple iterations of secret sharing scheme. A file is partitioned into multiple file shares, and one of them is taken as a new file to be further partitioned into smaller size with low additional computational cost and data expansion. The small-size file share is stored at user terminal as a necessary component to recover original file. It can be used in scenarios that user terminal, such as smart phone, is one of nodes in distributed storage systems. In this case, attackers cannot recover information through eavesdropping shares transmitted in network. Storage service providers cannot also obtain useful information through file shares stored online without the participant of the small-size file share at user terminal. Therefore, sensitive data can be protected confidentially. Copyright © 2013 John Wiley & Sons, Ltd.