zero-day exploit

An attack that takes place immediately after a security vulnerability is announced. If a user discovers a vulnerability, it might wind up on one or two blogs, and the news travels fast. If a software vendor finds it, the tendency is to keep it under wraps until it has a patch to fix it. However, in many cases, vendors have to announce the flaw because users may be able to avoid the problem by steering clear of a Web site or being sure to not open a certain e-mail attachment. See exploit.