Why are received spread spectrum signals resistant to interference?

Spread spectrum communications work by distributing the transmitted signal's energy across a very wide bandwidth using a specific pseudo-random algorithm. At the receiving end, the receiver uses the exact same algorithm to 'de-spread' the signal and recover the original data. Because interfering signals (or conventional narrowband signals) do not possess this specific pseudo-random algorithm, they are not de-spread by the receiver. Instead, the receiver's decoding process actually spreads the interference out, reducing it to low-level background noise. Distractors suggesting the use of high transmitter power are entirely backward, as spread spectrum signals typically operate with very low power density.