The main security vulnerabilities checked during a smart contract audit consist of:  1) Reentrancy Attack: This attack occurs when the smart contract glitches send external calls to an untrusted contract, leading to the drain of funds.  2) Front-running: Poorly created codes help scammers to know information before blockchain transactions and benefit from it.  3) Logic Errors: These errors are the most common form of vulnerability, including spelling and basic coding mistakes.  4) Integer Overflow and Underflow: Here, the smart contract performs incorrect execution of arithmetic operations, resulting in wrong calculations.  5) Timestamp Dependence: Contracts that highly rely on timestamps can favor miners to manipulate to a certain extent.