Non-malleability of One Time Pad Encryption Can anyone explain to me what the following means in relation to one time pad security?  It's from the book 'Serious Cryptography: A Practical Introduction' and my logic knowledge seems to have lost me here so I'm struggling :-

Given a ciphertext $C_1 = E(K, P_1)$, it should be impossible to create another ciphertext, $C_2$, whose corresponding plaintext, $P_2$, is related to $P_1$ in a meaningful way (for example, to create a $P_2$ that is equal to $P_1 \oplus 1$ or to $P_1 \oplus X$ for some known value $X$). Surprisingly, the one-time pad is malleable: given a ciphertext $C_1 = P_1 ⊕ K$, you can define $C_2 = C_1 \oplus 1$, which is a valid ciphertext of $P_2 = P_1 ⊕ 1$ under the same key $K$. Oops, so much for our perfect cipher.
The Problem

The One-Time Pad offers perfect secrecy. However, it does not protect the integrity or authenticity of the message - An adversary can flip bits of the ciphertext, and the receiver will have no way of detecting the manipulation. 

Consider the case where a single bit is sent encrypted with a One-Time Pad, used to indicate a "yes/no" value as to whether or not Alice wants to have lunch with Bob. If Mallory intercepts the message $C$ and computes $C \oplus 1$ and then sends that value to Bob instead, Bob will receive the opposite of Alice's intended message - and he will have no way of knowing that it has been tampered with.

The solution

Use a MAC to ensure the integrity and authenticity of the message.