according to different observation i think few ways are available for abusing bitcoins transections such as Technical weakness , Greedy peoples ro dishonest people , proper management. i would like to describe above mentioned quotatin in briefly
1. technical weakness: we know its a peer to peer transection system throgh confirmed way. within a few second a dishonest  person can get more money by fast  clicking when submit second payment of different recipient.
2. proper management: there is so many lack of proper management of human or account holders. so many hackers want to hack system for getting money because bitcoins holder don't have any insurance like bank account holders. even government don't follow rules and regulation for virtual currency holders.
So what you think about it ?