A Public Block-Chain relies a public ledger, this ledger is not centralised, but rather, is duplicated to every user on the network (similarly to a Google Doc).
The ledger is beyond the reach of hacking as it is updated in real-time. As the ledger holds all of the information regarding the number of tokens each member has in their Block-Chain wallet, and is widely distributed, there’s no need for third-party verification. The underlying strength of a Block Chain network is the immutable nature of the Cryptocurrency itself.
For the immediate future, it seems that Block-Chain will be adopted primarily for Crypto-Currencies. Bitcoin is still the most developed Block-Chain network mentioned in the media. However, Block Chain entrepreneurs are constantly working to harness this new form of network to numerous other uses, and venture capital firms are on the hunt for promising start-up companies which are developing such technologies.
While the concept of Crypto-Currencies is still being debated (and sometimes negated) by mainstream financial institutions, there is a general consensus that the application of Block-Chain technologies will affect many aspects of technology. See Wikipedia