A software regression is a software bug which makes a feature stop functioning as intended after a certain event (for example, a system upgrade, system patching or a change to daylight saving time). A software performance regression is a situation where the software still functions correctly, but performs slowly or uses more memory when compared to previous versions.
Regressions are often caused by encompassed bug fixes included in software patches. One approach to avoiding this kind of problem is regression testing. A properly designed test plan aims at preventing this possibility before releasing any software. Automated testing and well-written test cases can reduce the likelihood of a regression.
A software regression can be of one of three types: