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# System prepended metadata

title: Introduction to Smart Contract

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### Introduction to Smart Contract Security

Smart contracts are self-executing programs that live on the blockchain. They’re the backbone of decentralized applications (dApps), enabling everything from DeFi to NFTs. But with great power comes great responsibility — and risk. Because smart contracts often manage real assets (tokens, data, governance), vulnerabilities in their code can be costly. That require you as a developer to employ alot of measures to prevent your smart contract from been exploited.

**Why Smart Contract Security Matters**

- **Immutable Code**: Once deployed, smart contracts can’t be changed (unless specifically designed to be upgradable).
- **No Central Authority**: There's no admin to fix bugs after deployment.
- **Real-World Stakes**: Billions of dollars have been lost to bugs, hacks, and exploits.

**Common Vulnerabilities**
1. **Reentrancy Attacks**  
   An attacker repeatedly calls a function before the previous execution finishes, leading to draining funds. Reentrancy attack is very common in the Web3 space.

2. **Integer Overflows/Underflows** 
   Arithmetic operations exceeding type limits can lead to logic errors. Which case turn out to be an attack vector for a hacker.

3. ** Unprotected use of call or delegatecall**  
   Misusing low-level functions can give attackers control or destroy contracts.

4. **Access Control Issues**
Poor use of onlyOwner or admin modifiers can allow unauthorized access.

5. ** Front-running ** 
   Attackers monitor the mempool to exploit timing and gas manipulation.

**How to Improve Security**
- **Audit Your Code**: Either self-audit (using tool like slither or mythril )or hire professionals.
- **Use Proven Libraries**: E.g., OpenZeppelin for tokens and access control.
- **Test Thoroughly**: Unit tests, integration tests, and fuzzing.

**Security Best Practices**
- Always follow Checks-Effects-Interactions pattern.
- Use low level calls over with utmost care.
- Avoid storing secrets on-chain.
- Limit external contract calls.

**Conclusion**
Smart contract security isn't optional — it’s essential. As Web3 grows, so does the attention from hackers and malicious actors. Writing secure contracts and continuously educating yourself is part of being a responsible builder in this ecosystem.