Green’s Dictionary of Slang

1. (Aus. und.) a thief, a house-breaker.

1901

Truth (Sydney) 29 Sept. 7/3: They has a ball of string / Hooked on to the Cracker’s clobber, / Wot they pulls, so he can wing.

2. a safe-breaker.

1916		J. Lait ‘Canada Kid’ Beef, Iron and Wine (1917) 155: I was the son of a tough box-cracker an’ a whisky-drinkin’ counter-snatcher.
1976		W. Stevenson A Man Called Intrepid (1979) 369: The Cracker was a peteman, a safecracker with an encyclopedic knowledge of locks.
1998		P. Doyle (con. late 1950s) Amaze Your Friends (2019) 69: Tools of the trade: gelignite, hammers, chisels, drills [...] we’re having an early cracker night.

3. (US Und.) a safe.

1929

C.G. Givens ‘Chatter of Guns’ in Sat. Eve. Post 13 Apr.; list extracted in AS VI:2 (1930) 132: cracker, n. A safe.

4. a credit card computer fraudster.

2003

Observer Crime 27 Apr. 38: Poultney had become the victim of a ‘cracker’ [...] some crackers work in serious organised gangs.