Deleting anything
On the Internet is not possible.
Just look at the hoards of out-of-context-and-heavily-edited excerpts from threads which float around in any virtual group.
I've been seeing a lot of discussion recently about how such virtual communication removes many of the filters we would otherwise apply to our communications.
It's just going to take a few years before the dust settles and we all agree on appropriate protocols.
Deletion, however - no. Ain't never gonna happen. No way, no how. Make a careless statement in the quietest period of your virtual group's posting "day", erase it one minute later...and you can go to bed secure in the knowledge that the next day, it will be broadcast (edited and slanted to worst effect) far and wide.
Around the turn of the century, a grad student sent me a copy of his thesis to check. Like most electronic files of the day, the charts were embedded and the graphs were linked. Unfortunately, the accompanying data set of links included a picture of himself which left nothing to the imagination, alongside the other files (same first two alphanumeric characters, same file ending, very easy mistake).
I wouldn't have noticed it (not being concerned with the hard math, thank the gods) had I not wanted to cross-check his indices.
Oh, boy. I sent him a very quick text message and email, pro-actively wrote my other two colleagues that the file he'd sent them wasn't to be opened, danger of a virus or somesuch and erased the file from the server (something I didn't have the rights to do, either, but then, IT security on our campus was and is not quite what it should be).
Now, I never sent that jpeg on. He surely did not.
But I did view his thesis on one of the computers in our student union.
Somebody went through the cache for the program, pulled out the picture and by the next day, everyone on campus knew all there was to know.
This being Europe and he being over 18, nobody cared. But the lesson was one my colleagues and I repeat to incoming freshmen every semester. The internet is forever.