An alert box is a kind of dialog box which warns the user of a potentially serious problem.
Instances where an alert box might occur include the following situations:
- When the user runs out of hard disk space;
- When there is insufficient memory to open an application (very common before Mac OS X);
- When an application program has quit unexpectedly (related to this is a force quit);
- When an application encounters an error.
On systems prior to Mac OS X, the standard icon was that of a stop sign, with the words "STOP" replaced by a hand icon. On Mac OS X, an exclamation mark is more likely to occur.
Once the user dismisses the alert box, action should be taken; for examples, unnecessarily open applications should be quit; a restart may be necessary, etc.