Firms that specialize in gathering confidential information about companies for many uses, including trends in particular industries and companies. The expert-network firms collect this information from various sources, including current and former employees of a company. If this information is then used to buy or sell stock, perhaps by a hedge fund or other large investor looking for an information advantage, the trade can be considered insider trading, and the transmission of information that motivated the trade can be considered illegal tipping. See the FAQs
in the section SEC Law: Insider Trading.