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.
Adware
The term "adware" is frequently used to describe a form of malware (malicious software) which presents unwanted advertisements to the user of a computer. The advertisements produced by adware are sometimes in the form of a pop-up or sometimes in an "unclosable window".