An out-of-band patch is a patch released at some time other than the normal release time. Microsoft, for example, normally releases patches on the second Tuesday of every month. A patch, sometimes called a "fix," is a quick-repair job for a piece of programming.
The usual reason for the release of an out-of-band patch is the appearance of an unexpected, widespread, destructive exploit such as a virus, worm, or Trojan that will likely affect a large number of Internet users. A good example is a so-called zero-day exploit, which takes advantage of a security hole on the same day that the vulnerability becomes generally known, so there exists no elapsed time (zero days) between the discovery of the vulnerability and the first attack that comes as result of it.
When deciding whether or not to release an out-of-band patch, software vendors take several factors into account by asking themselves questions such as the following.
- Is this particular event serious enough to warrant the release of a patch out of the normal cycle?
- How widespread is the attack? How many people are likely to suffer adverse effects if we do not release a patch immediately?
- Has the vulnerability occurred close enough to the normal release date to make it reasonable to wait until then to release the patch?
- Will the rushed development and release of a quick patch likely disturb program functionality, perhaps producing more trouble than it resolves?
- Is the threat stable, or is it evolving (or likely to evolve) day by day?