I've always went by the case of two particular songs-1 "Werewolves of London" by Warren Zevon/ "All Summer Long" by Kid Rock and 2 "Super Freak" by Rick James/ "Can't Touch This" by MC Hammer.  If you listen to these pieces of music it sounds like Kid Rock used the exact backing track that Zevon made for "Werewolves" and just sang a new vocal track over it.  The same with the Rick James and MC Hammer tunes.  But I've never heard of any litigation in either of these cases (although there might be.  I just didn't hear of it).  I was always assured that it was because MC Hammer and Kid Rock changed the melody of their songs.  But I guess that's all changed now.
 
EDIT-Did some research on these.  Turns out Kid Rock paid Zevon's publishing co for the rights to use his track via sampling.  He also named Zevon and his Werewolves co writers as co composers of ASL.  Same thing for the MC Hammer/Rick James situation.
 
JB
 
 

markno999
 
Interesting comparison by Rick Beato below - The Gaye estate is suing Ed Sheeran for 100M claiming his song Thinking Out Loud is infringing Let's Get It On.   Look at the song as a whole, there may be some similarities and people have strong opinions about it. 
 
 

Mostly I wonder what Ed's plan is once she turns 70.