Social engineering and financial hacks are not fair game, and are "illicit" in the sense that crypto is obviously an international martial zone.
Exhaustively brute forcing a keyspace is valid, making your username an XSS to steal funds from an insecure page/downstream app is not valid.
Finding and leveraging an exploit in a contract is valid, both a paper/legal contract and a literal codified Eutherem contract. Flashing incorrect token prices on CoinMarketCap.com to take advantage of (unauthorized? grey) downstream screenscrapers and rugpulling affected tokens is NOT valid, but, admittedly murkier.