The Israel Securities Authority will be examining the legitimacy of measures that led the Tel Aviv Stock Exchange to rebound yesterday to a 2% gain moments before closing.

Right before closing, the Maof-25 index was down 1.4%. At the last moment NIS 20 worth of buy orders, probably streamed by speculators on the Msof-25 index, sharply reversed the trend.

Today is the expiry day for March options on the Maof index. Many Maof speculators yesterday wailed that the violent last-second shift yesterday did not give them time to respond.

An Israel Securities Authority spokesperson yesterday said that the intensity of the swing raises questions and that the authority is going to look into the matter.

Options on the Maof index always expire on the last trading Thursday of each month. Expiry Thursdays are usually marked by drastic trend shifts.

Three months ago a single Maof speculator managed to shift the index in his favor one second before the level of the index was finalized for the purposes of the expiry.

This event inspired the Securities Authority to change the rules. Beforehand the Maof level for the purposes of expiry was the one at exactly 9:45 in the morning on expiry Thursday. Now the final index is chosen at any moment in time between 9:45 and 10:00. The Securities Authority's concept was to foil speculators trying to shift the index at the last second, as the speculators cannot guess the precise moment at which the index is chosen.