"While we are still in the process of an ongoing investigation, we recognize that the information security environment is evolving rapidly," Steinhafel said in a statement.
Target will be facing fallout from the theft for a while. The company said last week that its fourth-quarter profit fell 46 percent on a revenue decline of 5.3 percent as the breach scared off customers.
Target said sales have been recovering as more time passes since news of the breach. But the company expects business to be muted for some time. It issued a profit outlook for the current quarter and full year that was below Wall Street estimates as it faces hefty costs related to the breach.
Steinhafel told investors last week that Target has updated shoppers early and often on the investigation and is offering free credit monitoring for a year for any customer shopping at a Target store who wants it.
The company is also equipping its locations with more security technology. Target is accelerating its $100 million plan to roll out chip-based credit card technology, which experts say is more secure than traditional magnetic stripe cards.
Target's breach may eventually eclipse the biggest known data breach at a retailer, one disclosed in 2007 at the parent company of TJ Maxx that affected 90 million records.
In a posting last week on a company blog, Steinhafel said, "In the weeks ahead, we hope to understand more about how this attack happened. And will use what we learn to inform our guests, make Target a safer place to shop and to drive change across the broader retail industry."
In a letter to Steinhafel furnished by Target, the outgoing Chief Information Officer Jacob said that resigning was a "difficult decision," but she said that "this was a time of significant transformation for the retail industry and for Target." She did not mention the data breach.
During her tenure as chief information officer, Jacob received attention for helping Target respond more quickly to shoppers' shift to researching and buying on mobile devices.
That included a mobile app called Cartwheel, which combines social networking and discounts. She also oversaw Target's innovation lab that opened last May in San Francisco. The lab looks at futuristic technology, such as how wearable gadgets like smart watches might be used in it stores.
Shares of Target are down 87 cents to $60.46 in midday trading Wednesday. The stock is down a little over 3 percent since the breach was disclosed. (Click here for the latest quote.)
—The Associated Press
CORRECTION: This story has been updated to reflect Beth Jacob's former job title.