Sanders says security measures weren't reinstated properly following an October 2009 upgrade. Sanders says the company fixed the problem as soon as it became aware of it.
Applicants under age 65 who were applying for individual policies were affected by the breach. Attorney Dan Robinson, who is representing plaintiffs whose information was in jeopardy, said files were not secured for a five-month period.
Robinson says it's unknown how many people worldwide may have accessed the site illegally. Sanders said that according to Anthem's survey, the vast majority of unauthorized access was from the plaintiff and her attorneys.
Sanders said the attorneys downloaded some of the information from the site, but had since relinquished it.
Anthem sent letters to customers who may have been affected and offered a free year of identity protection services.
The Associated Press contributed to this report.