Q:

Where did the term "flame war"/"flaming" come from?

I found this term on the history of Tanenbaum and Torvalds debate, but I couldn't find the origin of the term. 
I've understood the meaning (from UrbanDictionary):

A flame war is a heated argument between two individuals, that results
  in those involved posting personal attacks on each other during or
  instead of debating the topic at hand.

So, what is the origin?

A:

to flame OED figurative

b. Of persons: To burn (with envy, fury, indignation, etc.); to look
  angrily or passionately upon. to flame out, up: to break out into
  open anger or indignation; to ‘fire up’.  

As in:

1548   N. Udall et al. tr. Erasmus Paraphr. Newe Test. I. Matt. xxii.
  f.    'Whiche wholy flame with enuy and hatred'.

and

1681   J. Crowne Henry VI i. iv. 49   I flame with fury to be at it.

More recently:
intr. slang (orig. and chiefly Computing). To rant, argue, or harangue, esp. via an electronic medium (such as e-mail or postings to a newsgroup); to send an inflammatory, abusive, or (esp. in early use) inconsequential e-mail or posting, usually as a hasty response or in a rapid, angry exchange. Also trans.: to send (a person) such a message. Cf. flame n. and adj.
as in:

1981   CoEvolution Q. Spring 31/1   Flame, to speak incessantly and/or
  rabidly on some relatively uninteresting subject or with a patently
  ridiculous attitude.

