1. Wikipedia,
http://en.wikipedia.org/wiki/Cloud_service
2. NETMARKETSHARE,
http://www.netmarketshare.com
3. iCloud: Syncing,
http://www.macworld.com/article/1162953/icloud_syncing.html
4. Hyunji, C., Jungheum, P., Sangjin, L., Chulhoon, K.: Digital Forensic Investigation of Cloud Storage Services. Digital Investigation (2012)
5. Mark, T., John, H., David, G., David, L.: Forensic investigation of cloud computing systems. Network Security 2011(3), 4–10 (2011)