A letter from the M&S hackers landed in my inbox - this is what happened next

Almost daily, my phone pings with messages from hackers of all stripes.
The good, the bad, the not-so-sure.
I've been reporting on cyber security for more than a decade, so I know that many of them like to talk about their hacks, findings and escapades.
About 99% of these conversations stay firmly locked in my chat logs and don't lead to news stories. But a recent ping was impossible to ignore.
"Hey. This is Joe Tidy from the BBC reporting on this Co-op news, correct":[]}