"to cut roughly, cut with chopping blows," c. 1200, from verb found in stem of Old English tohaccian "hack to pieces," from West Germanic *hakkon (source also of Old Frisian hackia "to chop or hack," Dutch hakken, Old High German hacchon, German hacken), from PIE root *keg- "hook, tooth." Perhaps influenced by Old Norse höggva "to hew, cut, strike, smite" (which is unrelated, from PIE *kau- "to hew, strike;" see hew).
The slang sense of "cope with" (as in can't hack it) is recorded in American English by 1955, with a notion of "get through by some effort," as a jungle (phrase hack after "keep working away at" is attested from late 14c.). To hack around "waste time" is U.S. slang, by 1955, perhaps originally of golfers or cabbies. Related: Hacked; hacking.
"person hired to do routine work," c. 1700, ultimately short for hackney "an ordinary horse, horse for general service (especially for driving or riding, as opposed to war, hunting, or hauling)," c. 1300. This word is probably from the place name Hackney, Middlesex. Apparently nags were raised on the pastureland there in early medieval times. Extended sense of "horse for hire" (late 14c.) led naturally to "broken-down nag," and also "prostitute" (1570s) and "a drudge" (1540s), especially a literary one, one who writes according to direction or demand. Sense of "carriage for hire" (1704) led to modern slang for "taxicab." As an adjective, 1734, from the noun. Hack writer is first recorded 1826, though hackney writer is at least 50 years earlier. Hack-work is recorded from 1851.
HACK. A hackney coach. The term hack is also frequently applied by women to any article of dress, as a bonnet, shawl, &c., which is kept for every day use. [Bartlett, "Dictionary of Americanisms," 1848]
Meaning "one who gains unauthorized access to computer records" is attested by 1975, and this sense seems to suggest hack (v.1), but the computer use is said to be from slightly earlier tech slang sense of "one who works like a hack at writing and experimenting with software, one who enjoys computer programming for its own sake," reputedly a usage that evolved at Massachusetts Institute of Technology (however an MIT student from the late 1960s recalls hack (n.) being used then and there in the general sense of "creative prank." This suggests rather a connection with hack (n.2) via the notion of "plodding, routine work." There may be a convergence of both words here.