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# Tutorial 63: Balance Check Using ==

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In Solidity smart contracts, performing checks on token balances is a common practice to ensure that transactions proceed as expected. However, developers often rely on exact balance comparisons using the `==` operator, which can introduce a significant vulnerability. This approach can be exploited by external actors who send tokens to the contract, leading to unexpected balance changes. When the contract checks for an exact balance match, it may fail due to these additional tokens, potentially causing a **Denial of Service (DoS)** situation where the contract becomes unusable.

This tutorial will explore how this vulnerability arises, its impact on smart contracts, and how developers can mitigate the risks associated with exact balance comparisons. By understanding these vulnerabilities, you can implement more secure balance-checking mechanisms to prevent attackers from locking critical contract functionality.