Wal-Mart investors would do well to remember that where there's smoke there's fire.

This past weekend's report of bribery by the retailer's Mexican subsidiary is likely to be only the beginning of the bad news for the company. (Read the fully story about the allegations of bribery against Wal-Mart.)

That at least is the conclusion I draw from reviewing a major academic study into the impact of anti-bribery enforcement actions. Upon studying a large number of bribery cases over the years, the study's authors found that the market's reaction to reports of bribery tends to be minuscule except when the bribery is accompanied by other financial misdeeds.

Since shares of Wal-Mart (WMT) fell an incredible 4.7% in Monday's trading, equivalent to $10 billion of market capitalization, the market is clearly betting that there is more bad news still to come out.

The study in question is entitled "The Impact of Anti-Bribery Enforcement Actions on Targeted Firms." Its authors are three finance professors: Jonathan Karpoff of the University of Washington, Scott Lee of Texas A&M, and Gerald Martin of American University.

The researchers studied all bribery enforcement actions initiated against publicly traded companies by the Justice Department or the SEC between 1978 and 2011. This sizeable sample enabled the researchers to estimate the unique impact of a bribery charge when it is not accompanied by other financial misdeeds, such as financial misrepresentation or fraud.

Incredibly, the researchers found that, in the case of "bribery-related announcements that are not contaminated by contemporaneous charges for financial misrepresentation," the market's initial reaction is a statistically insignificant drop of just 0.47%. That's one-tenth the market's reaction to the news about Wal-Mart.

Might Wal-Mart's big plunge simply be overreaction? It's always possible, Professor Karpoff said in an interview Monday afternoon. But he is inclined to discount that possibility, since that is not the pattern that emerged from he and his co-authors' study of the market reaction to prior bribery announcements.

On the contrary, he said, that historical pattern suggests that "investors are betting that there is more bad news to come out" about Wal-Mart.