According to company spokesman Rich D'Amato, customer service records of about 200 AOL users were compromised when "a very limited number of employees" in the US downloaded a "trojan horse" program, loosely described as a virus.
None of those customers whose details were compromised were believed to be Australian, he said.
AOL has already deployed additional security measures, D'Amato said. He could disclose details of those measures for security reasons.
All those possibly affected have been contacted directly by AOL, D'Amato said.