"Examples of insider trading cases that have been brought by the SEC are cases against:

Corporate officers, directors, and employees who traded the corporation's securities after learning of significant, confidential corporate developments;

Friends, business associates, family members, and other 'tippees' of such officers, directors, and employees, who traded the securities after receiving such information;

Employees of law, banking, brokerage and printing firms who were given such information to provide services to the corporation whose securities they traded;

Government employees who learned of such information because of their employment by the government; and

Other persons who misappropriated, and took advantage of, confidential information from their employers."

Apr. 19, 2001 - US Securities Exchange Commission (SEC) 

"The following are examples of illegal insider trading:

The CEO of a company sells a stock after discovering that the company will be losing a big government contract next month.

The CEO's son sells the company stock after hearing from his dad that the company will be losing the big government contract.

A government official realizes that the company will lose a big government contract, so the official sells the stock.

...If someone is caught 'tipping' an outsider with material nonpublic information, that tipster can also be found liable. The SEC uses the 'Dirks Test' to determine if an insider gave a tip illegally. The test states that if a tipster breaches his or her trust with the company and understands that this was a breach, he or she is liable for insider trading."

May 20, 2008 - Investopedia