The probe comes amid a new bout of turmoil that has gripped investors. Questions have been swirling about the financial health of mortgage giants Fannie Mae and Freddie Mac as well as Lehman Brothers Holdings Inc.
Earlier this year, a run on Bear Stearns pushed the investment bank to the brink of bankruptcy and into a takeover by JPMorgan Chase. Bear officials blamed market rumors for the run.
The investigation will be conducted by the SEC's Office of Compliance Inspections and Examinations as well as the Financial Industry Regulatory Authority and New York Stock Exchange Regulation Inc.
Cox said the probe will provide an opportunity to make sure brokers and investment advisers have "appropriate training for their employees and sturdy controls in place to prevent intentionally false information from harming investors."
By law, brokers and investment advisers must have procedures in place to prevent market manipulation and other violations. Investigators will focus on such procedures, or controls, and whether "they are reasonably designed to prevent the intentional creation or spreading of false information intended to affect securities prices or other potentially manipulative conduct," the agency said.
The probe is separate from SEC's investigations, already under way, into alleged intentional manipulation of securities prices through "rumor-mongering and abusive short selling," the agency said in a statement.
