Yahoo’s Mayer to activist investors: Back off by Miguel Helft @FortuneMagazine 11:40 AM EDT E-mail Tweet Facebook Google Plus Linkedin Share icons In a spirited defense of her tenure as CEO of Yahoo, which is under attack from activist investor Starboard Value, Marissa Mayer said Tuesday that she is confident the company is on the right track. It has gained market share in mobile where it finally has “material” revenue of approximately $200 million. It built a $250 million business in native ads in just a few months. It maintained market share in search. And it is returning plenty of cash to shareholders. “We’ve come really far, really fast,” Mayer said during a conference call with investors. “We have built a truly excellent team that is up to the task. We have achieved much more than many people realize.” Mayer noted—not once or twice, but three times—that Yahoo YHOO has repurchased $7.7 billion of its shares, or nearly 24 percent of total, more than the company had committed to do. The repurchases—at an average price far below Yahoo’s current value—were financed through various sources, including sales of shares of Alibaba BABA , which have driven Yahoo’s value over the past year, some financial engineering like “hedges” against the value of the Japanese yen, and even from some of the cash flow Yahoo’s business generates. That $7.7 billion is money that went back into the pockets of shareholders, and dwarfs the $1.6 billion that went out the door in acquisitions. While Mayer didn’t mention Starboard by name, she was clearly responding to the activist fund’s claims that her acquisitions, most notably the $1.1 billion she spent on Tumblr, has been ineffective. While many say it’s too early to tell whether those acquisitions will pay off, Starboard wants those acquisitions stopped. Mayer answer? Not a chance. Mayer said Tumblr has grown dramatically by all metrics: traffic, number of blogs and time spent by users on the site. And it’s on track to generate $100 million in revenue in 2015. She then defended her acquisition strategy, which she says has three pillars: talent acquisitions, to bring in top flight engineers in mobile and other growth areas; building block acquisitions, which infuse Yahoo with technology it needs to replace its aging infrastructure; and strategic acquisitions like Tumblr. “Across talent acquisitions, building blocks, and strategic acquisitions, we have funneled our resources directly into mobile, social, native, and video, and we have growing users, traffic, and revenue tremendously,” Mayer said. “Our recent acquisitions have been instrumental in replacing and will eventually outpace our declining legacy revenues.” And if the strategy has worked so far, Mayer sees no reason to change it. “In summary, we have a clear M&A strategy and a principled process for reviewing M&A opportunities,” Mayer said. “We will continue to seek opportunities here, and we will be smart about it.” On any other day, all this might have fallen on deaf ears. But on Tuesday, investors may have been in a listening mood because Mayer, after presiding over a string of revenue declines as Yahoo’s advertising business deteriorated, announced that Yahoo’s sales had actually grown in the third quarter. The gains were feeble—a mere 1% percent—but enough to surpass modest forecasts. And better yet, some of the growth was in areas in which Mayer has been investing, like mobile and native ads. No one, not even Mayer, is ready to claim Yahoo’s fortunes have turned around. “One quarter does not a year make,” Mayer said. “Like and company in transition we will have our ups and downs.” Consider yourself warned. But the upshot was clear: Yahoo shares climbed 3.7% in after hours, after rising 2.29% in regular trading. That adds up to a roughly 6% gain for the day. For Mayer, this doesn’t amount to vindication. It’s not a vote of confidence that her strategy will work. It is, however, a bit of breathing room as she tries to turn modest gains into something more meaningful.