Use of whom

[claig]

Saw a Channel 4 News web page with a headline
"Who is attacking who?"

Shouldn't it be "who is attacking whom?"

Keep seeing similar things where 'whom' is not being used. Does it not matter anymore, have the rules fallen into disuse?

What IS the rule of whom usage? I think I get it right in my usage most of the time but not 100% and been meaning to ask this question for a whole... Thanks!

That's a good hint about the him/her for whom. I didn't know that one. I just tend to use whom when it is the object rather than the subject.