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.
Mahdi (malware)
Mahdi is computer malware that was initially discovered in February 2012 and was reported in July of that year. According to Kaspersky Lab and Seculert (an Israeli security firm which discovered the malware), the software has been used for targeted cyber espionage since December 2011, infecting at least 800 computers in Iran and other Middle Eastern countries. Mahdi is named after files used in the malware and refers to the Muslim figure.