Each time an N.D.A. is signed, it stalls the conversation for a week because of the legal work involved, Mr. Hwang said, and over time, that can give a competitor the opportunity to enter a market first. “In the life of a start-up company,” he said, “you might have to sign 30 to 50 N.D.A.s. That’s a week each time and a year of holdups. The risk of going slow is bigger than the risk of being copied.”

When Mr. Moeck was told that Kleiner Perkins does not sign N.D.A.s, he decided to pitch his start-up anyway. “I felt O.K. about it because the investor was referred by a trusted friend and Kleiner is a very well-known firm,” he said. Mr. Moeck also felt that even if Zynga did learn what he was doing, the company had become too big to execute quickly. “I thought, regardless of what Zynga heard or thought, we had the better chance of being successful in our category,” he said. He was also hoping that disclosure might open doors. “Although we didn’t want Zynga to copy us,” he said, “we did want them to be aware of what we were doing in case there was an opportunity to partner with them.”

In the end, Kleiner did not offer financing to Moeo, although the company did manage to raise $500,000 from angel investors. It continues to ask investors to sign N.D.A.s, but has yet to persuade any to do so.

Below are some guidelines to consider. They apply when engaging not just investors, but also manufacturers, partners and even customers.

DO NOT ASK UNLESS YOU HAVE SOMETHING TO PROTECT. Chris Schultz, an entrepreneur and partner in the angel investment fund Voodoo Ventures in New Orleans, said: “Everyone thinks their idea is extremely unique, but the idea is really 1 percent of the value. The value is in the execution.”

Paul A. Jones, co-chairman of the venture best practice group at the law firm Michael Best & Friedrich in Milwaukee, said there was no reason to share proprietary information during an initial 20-minute pitch anyway. “And I’ve never known a reputable investor to steal an idea and create a company around it,” he said.

KNOW YOUR AUDIENCE. Before making a pitch, research the background of your audience. “Think through who you are sharing your ideas with,” said Patrick Riley, head of Global Accelerator Network, a group of 50 start-up accelerators worldwide. “Unless the investor is very well known, have a reference or two. People will say they are investors when they aren’t, so ask what other deals they have done, and then call those companies to ask about the deal. Do they trust this investor?”