Active money managers keep an approved list" around to purposely limit the securities they can pick in a given fund. Let's say the theme of one fund is "Senator Approved" - that means no "sin stocks" - no tobacco, no adult entertainment stocks, no ... caffeine? No... polluters? No... Republican CEOs? That list could get pretty narrow pretty fast.
In large mutual fund complexes, sometimes an analyst will come across inside information and they must halt trading or the potential of trading in a given name. e.g., they hear in the hallway that Microsoft is about to buy Disney directly from Bill Gates, whose high pitched voice distinctly cuts through long hallways. They must take DIS and MSFT off the approved list (their traders usually have electronic gates managed by in-house lawyers so that they are physically prevented from trading in a restricted security) until that information comes public.