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.
The Bubble Boy (Seinfeld)
On November 10, 1999, a computer virus named "BubbleBoy" was discovered, apparently named after this episode. This was the first malware of its kind, having been actually able to activate itself (via an embedded Visual Basic script) upon the recipient opening the e-mail contents, as opposed to running an attachment. As such, in spite of not actually being dangerous, the virus changed the concept of antivirus technology.