## 🌭 security tips

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* `tx.origin` needs to bere placed by `msg.sender`, otherwise any contract you call can act on your behalf.
* inline assembly should be used only in rare cases.
* unclear semantics: `now` is alias for `block.timestamp` not current time; use of low level `call`, `callcode`, `delegatecall` should be avoided whenever possible; use `transfer` whenever failure of ether transfer should rollnack the whole transaction.
* beware of caller contracts: `selfdestruct` can block calling contracts unexpectedly.
* invocation of local functions via `this`: never use `this` to call functions in the same contract, it only consumes more gas than normal call.
* transferring Ether in a for/while/do-while loop should be avoid due to the block gas limit.
* erc20 `decimals` should have `uint8` as return type.

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