Yahoo said it would consider keeping other types of information about its users too.
For example, on Thursday, Yahoo said it had joined an alliance between Vivendi Universal and Sony.
But Yahoo said the system was not yet paying off and that a further roll-out was on hold while changes were made.
Yahoo said it did not know for sure that the file had been taken but told AFP it could not "deny the possibility".
Yahoo said it is shutting down the Summly app, which was downloaded less than one million times, and incorporating its technology into other Yahoo services.
Yahoo said it was continuing to make progress on efforts to expand into the fast-growing mobile internet market, and to increase the amount of video advertising on the site.
Yahoo said it doesn't comment on individual account holders.
Yahoo said it has developed more sophisticated formulas to determine which topics are most likely to appeal to different people so the news feed can be fine-tuned to cater to different tastes.
Yahoo said that it would hold onto web data for as long as EU law required - but the firm did not say what it would do with the information beyond the 24 months demanded by the law.
At the same time, the blogging service offers several advantages Yahoo executives said could benefit Yahoo, like a successful track record snagging users on mobile devices.
"It's difficult to know, difficult to know, " a Yahoo employee said when asked about the matter.
Yahoo has said that a partnership with Microsoft is facing delays as it awaits improvements in technology.
Yahoo Japan, jointly owned by mobile firm Softbank and Yahoo, said it had tightened security measures in the wake of the attack and was investigating to ensure attackers could not repeat the theft.
If AOL's services work together more fully, "it opens the door for us to argue for interoperability, " Brian Park, a senior instant messenger producer at Yahoo, said in Tuesday's edition of the Wall Street Journal.
Yahoo Chief Financial Officer Ken Goldman said Yahoo expects its acquisition to add "relatively modest" revenue to its top line in the second half, when the deal is expected to close, with its contribution ramping up next year.
In an interview with Paris-based daily newspaper La Liberation published Friday, Jerry Yang, co-founder of Yahoo, said that, while the company's French subsidiary would respect French law, he doubted that French courts could make a U.S. company block French users from accessing the content of its U.S. servers.
"As you get closer to the end of the year, people re-examine their lives, " said Yahoo!
Ms Mayer said Yahoo would now work with Tumblr to create ads that "are seamless and enhance the user experience".
Dan Peters, head of Yahoo Answers, said in a statement that the company tries to guide users to helpful answers through a rating system.
WSJ: Quora and Others Are Racing to Fill Gaps Left by Google
People familiar with the matter said Yahoo believes it could help Tumblr bring in more money by selling ads, boosting its own revenue in the process.
Earlier Tuesday, Microsoft Chief Executive Steve Ballmer said Yahoo!'
Jeff Embersits, an analyst at Shareholder Value Management said Yahoo!
Earlier Tuesday, Microsoft Chief Executive SteveBallmerSteve Ballmer said Yahoo!'
But in February, Mayer also said Yahoo will be better served with just 12 to 15 mobile applications, down from a "scattered" portfolio of as many as 75 different programs in recent years.
One MWC exhibitor GENBAND, a U.S.-based company that provides technology which can be used to create remote working environments, said Yahoo's move was understandable, but the problems it faces could be overcome with better technology.
Marc Musgrove, Cisco's global communications director, said Yahoo's announcement was unfortunately timed as it came just days ahead of the March 4 start of the third annual Telework Week, a Cisco-backed global initiative to encourage remote working.
Anne Espiritu, a Yahoo spokeswoman, said in a statement that Ms. Mayer is "carrying out a careful review of the company's business" and is looking at "potential strategy changes to Yahoo's current plans" along with fellow Yahoo directors.
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