A skirmish has erupted between a firm marshalling the huge securities class action against McKesson HBOC Inc. and another one trying to outflank it.

In an attempt to break away from the class in what could be one of the largest securities settlements ever, Chicago’s Much Shelist Freed Denenberg Ament & Rubenstein is soliciting plaintiffs for individual suits against the health care giant after a judge gave lead plaintiff status to a New York firm.