Instant Messages

I have one question about the alleged 52 instant message exchanges that ABC News has in its hands. Who saves and records IM exchanges for posterity? I mean: I know how emails are saved and forwarded; it happens automatically. But I was unaware that IM interactions have some permanent record that can be retrieved after the fact. Is there such a possibility? Or did someone keep saving and recording these IM exchanges at the time - presumably the teens involved? It's just an empirical question. But if these exchanges had to be taken down and recorded at the time, then it seems there are further questions to be asked about their provenance.