The breach began on Nov. 27, was confirmed on Dec. 15, and ended on Dec. 18. The company initially said 40 million credit and debit card accounts were affected, but its investigation subsequently revealed that a separate set of data, stored elsewhere and covering 70 million accounts, also had been stolen.

Jacob started with Target in 1984 as an assistant buyer. She left in 2002 then returned to the company in 2006. She was appointed CIO in 2008.

In an emailed statement, Gregg Steinhafel, chairman, president and CEO of Target, confirmed that the company is seeking a new CIO. "While we are still in the process of an ongoing investigation, we recognize that the information security environment is evolving rapidly," he said. "To ensure that Target is well positioned following the data breach we suffered last year, we are undertaking an overhaul of our information security and compliance structure and practices at Target. As a first step in this effort, Target will be conducting an external search for an interim CIO who can help guide Target through this transformation."

Steinhafel said Target will be "elevating the role of the chief information security officer" and filling the position externally. He also said the company plans to look for a chief compliance officer outside the company. In addition, he said Target is working with Promontory Financial Group to assess its systems, infrastructure, business processes, and talent.