Securities on HOLD/Restricted List

Can someone throw some light on the circumstances wherein a brokerage/investment banking division of a firm places a security on Hold or Restricted List? What exactly is meant by hold/restrict list?

They only give out factual information about the company . If I Bank has a potential deal coming up and if a negative view some what spoil the relatoinship . the securiteis can be put on a restricted list . the research analyst can only give out factual information of the company. this would be for the sell side for the buy side if there is a potential deal or the bank is the book runner , market maker , trading on the prop desk might be considered insider , the securities would be put on a restricted list