比特币节点接收到一个区块以后，都会进行校验和确认，如下参考网络图：

关键看看对区块中的交易进行进一步的校验代码：
1.// First transaction must be coinbase, the rest must not be
2.if (vtx.empty() || !vtx[0].IsCoinBase())

3. return error("CheckBlock() : first tx is not coinbase");
   4.for (int i = 1; i < vtx.size(); i++)
4. if (vtx[i].IsCoinBase())
5. return error("CheckBlock() : more than one coinbase");

6. 8.// Check transactions 循环检查所有的交易，这一步骤很关键，所以交易不能随便改，大家都在检查
   9.foreach(const CTransaction& tx, vtx)

7. if (!tx.CheckTransaction())
8. return error("CheckBlock() : CheckTransaction failed");

9. 13.// Check proof of work matches claimed amount
   14.if (CBigNum().SetCompact(nBits) > bnProofOfWorkLimit)

10. return error("CheckBlock() : nBits below minimum work");
    16.if (GetHash() > CBigNum().SetCompact(nBits).getuint256())
11. return error("CheckBlock() : hash doesn't match nBits");

12. 19.// Check merkleroot
    20.if (hashMerkleRoot != BuildMerkleTree())

13. return error("CheckBlock() : hashMerkleRoot mismatch");