Some big companies have had a surprise during their earnings conference calls this quarter -- and it has nothing to do with the weak economy.

At least seven times just the past three weeks, a mystery caller has cleverly insinuated himself into the normally well-manicured ritual of the quarterly calls. As top executives of publicly traded companies respond to securities analysts' questions about their balance sheets, he impersonates a well-known analyst to get called upon. Then, usually declaring himself to be "Joe Herrick...