Gremlin event or Hacker!
Days starting off well - jsut sitting at home PC and Dropbox popped up a msg saying a file (egrep.exe) had been deleted from a folder (It was part of the Arduino software package)
Went into Dropbox site and looked at events and it named which school where the instruction to delete came from. (Which I'm not at)
Very strange considering its a technical folder that no-one except me knows about but makes me think has this sort of thing happened before - I only noticed this one because I was sitting at a machine at the time!
Has my great "Security by obscurity" defences been breached :)
Could be an antivirus scan being a bit over eager.
That is a good explanation of an unexplained event : )
Ill check the clam antivirus log when I'm next in.