Malware
Malware authors target bugs, or loopholes, to exploit. A common method is exploitation of a buffer overrun vulnerability, where software designed to store data in a specified region of memory does not prevent more data than the buffer can accommodate being supplied. Malware may provide data that overflows the buffer, with malicious executable code or data after the end; when this payload is accessed it does what the attacker, not the legitimate software, determines.
Hajime (malware)
Hajime (Japanese for "beginning") is a malware which appears to be similar to the Wifatch malware in that it appears to attempt to secure devices.
Hajime is also far more advanced than Mirai, according to various researchers.