在C#中,为什么在内存中固定密钥更安全？

固定密钥有什么好处？我很确定有一个 – 一个非常聪明的开发人员,曾经一度提到过,这是我们软件安全的重要一步.来自MS article的相关代码.

static void Main()
{
    // Must be 64 bits,8 bytes.
    // Distribute this key to the user who will decrypt this file.
    string sSecretKey;

    // Get the key for the file to encrypt.
    sSecretKey = GenerateKey();

    // For additional security pin the key.
    GCHandle gch = GCHandle.Alloc( sSecretKey,GCHandleType.Pinned );

    // Encrypt the file.        
    EncryptFile( @"C:MyData.txt",@"C:Encrypted.txt",sSecretKey );

    // Decrypt the file.
    DecryptFile( @"C:Encrypted.txt",@"C:Decrypted.txt",sSecretKey );

    // Remove the key from memory. 
    ZeroMemory( gch.AddrOfPinnedObject(),sSecretKey.Length * 2 );
    gch.Free();
}