The

New York Stock Exchange

, in a somewhat unusual move, sought to lower the pitch of media speculation about its investigation into potential trading violations by specialist firms.

In a statement posted on its Web site, the NYSE said that contrary to some reports, it isn't investigating allegations of front-running by specialist firms that handle trading on its exchange floor. Rather, the NYSE said, the investigation is more limited in scope and the allegations of wronging are not as serious as some have made them out to be.

The NYSE said it's looking at whether some specialists may have violated the exchange's negative obligation rule, which requires them to "stand out of the way'' when a buyer and seller agree on a price for a stock. The exchange said it is looking into a number of instances in which specialists might have violated that rule by stepping in and buying stock from a seller at one price and then reselling it to a buyer at slightly higher price.

This differs from front-running because it doesn't involve a specialist trading for his own book, but rather just widening the spread in a sale he brokers.

The seven specialist firms that oversee trading on the Big Board are permitted to make stock trades for their own account, but not at the expense of their customers.

To some, the NYSE's distinction between what constitutes front-running and the negative obligation rule might sound like semantics. But the exchange said it matters because front-running is a more significant fraud and potentially can generate much bigger illegal gains for a specialist.

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"We emphasize that at this time no one has been charged with any violations,'' said the NYSE. "Nor is there any certainty that there was improper activity in all the stocks currently being reviewed.''

The NYSE's statement gave a lift to shares of two specialists firms that have taken a beating since the investigation became public. Shares of

LaBranche

(LAB)

rose 84 cents, or 5%, to $17.13. The stock of

Van Der Moolen

(VDM)

rose 64 cents, or 7%, to $9.70.