Hub Token

Description: As it presently is constructed, the contract is vulnerable to the allowance double-spend exploit, as with other ERC20 tokens. Exploit Scenario: 1. Alice allows Bob to transfer N amount of Alice's tokens (N>0) by calling the approve() method on Token smart contract (passing Bob's address and N as method arguments) 2. After some time, Alice decides to change from N to M (M>0) the number of Alice's tokens Bob is allowed to transfer, so she calls the approve() method again, this time passing Bob's address and M as method arguments 3. Bob notices Alice's second transaction before it was mined and quickly sends another transaction that calls the transferFrom() method to transfer N Alice's tokens somewhere 4. If Bob's transaction will be executed before Alice's transaction, then Bob will successfully transfer N Alice's tokens and will gain an ability to transfer another M tokens 5. Before Alice notices any irregularities, Bob calls transferFrom() method again, this time to transfer M Alice's tokens.

Every Solidity file specifies in the header a version number of the format pragma solidity (^)0.4.*. The caret ( ) before the version number implies an unlocked pragma, meaning that the compiler will use the specified version and above, hence the term "unlocked."