Poor Key Management
Lost private key, no back up
Bitomat was a Polish Bitcoin exchange that shut down around the same time as MyBitcoin, claiming to have accidentally deleted users’ 17,000 Bitcoins and declaring itself up for sale for that amount before resuming trading shortly thereafter. Supposedly, during a server restart, the remote Amazon service that housed Bitomat.pl’s wallet was wiped. No backups were kept, and Mt. Gox later bailed out Bitomat.pl. Ultimately, neither the exchange’s customers nor the original owners suffered any loss from the incident.