CAUTION: NOT A TEACHER
(1) "Sneak is a word of mysterious origin. It first turns up in Shakespeare.
Sneak not away, sir, for the friar and you must have a word.
-- Measure for Measure, 1605"
(2) "Sometime in the late 19th century a variant irregular form, snuck, began to
appear in the United States."
(3) Occurence in British English is rare but not unknown."
Source: Webster's Dictionary of English Usage (1989).
(4) "The standard past form is sneaked. Surprisingly, though, snuck appears
half as often in American writing as sneaked."
Source: A Dictionary of American Usage (1998) by Bryan A. Garner, whom some people call the "American Fowler."
P.S. I forgot to mention that Webster's Dictionary of English Usage thinks that
eventually "snuck" may win the battle because it seems to be popular with the