– Likely a misspelling or leetspeak for "Hack us" or a reference to "HackForums" (sometimes abbreviated HF). In underground slang, "hackus" can also relate to being accused of hacking ("hackusations"). More commonly, it's part of tool names like "Hackus Email Checker" — a rumored credential testing utility.
: Many email providers offer a feature to review recent account activity. This can include checking the "Sent" and "Deleted Items" folders for emails you didn't send, as well as looking for any unfamiliar login locations or devices in your account's security settings. hackus mail access checkerzip hot