Production data in testing

Copying real data into a test environment extends production sensitivity into places with production's protection removed.

Test systems have looser access, fewer controls, more people with administrator rights and far less monitoring, because that is what makes them usable for testing. The data inside is exactly as sensitive as it was in production. It is one of the most common ways real customer information ends up somewhere it was never risk-assessed, and it is almost always done in good faith to make testing realistic.