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You Could Have a Yahoo Account and Not Know It

If you play fantasy sports, post photos on Flickr or blog at Tumblr, then you have a Yahoo account.
The Yahoo logo is shown at the company's headquarters in Sunnyvale
The Yahoo logo is shown at the company's headquarters in Sunnyvale, California. REUTERS/Robert Galbraith

Think the Yahoo hack doesn’t affect you? Think again. Because if you play fantasy sports, post photos on Flickr, or use Yahoo Finance, then you have a Yahoo account. Which means your private information is at risk.

Fantasy sports players — a particularly rabid crew — were quick to respond to news that they could be part of the recent megahack that included breached information for over a billion accounts.

“Hackers can have all my Yahoo info if they want, but if they change my fantasy football lineup, it’s war,” tweeted one.

A Yahoo representative told NBC News that as of last week, there were 225 million active Yahoo Mail accounts, which means various other Yahoo accounts were likely included in the breach.

Related: After the Mega-Hack, Why Haven't We Heard From CEO Marissa Mayer?

Even if you have a Yahoo account but have left it dormant, you may be at risk. With many people using similar passwords and security questions across multiple sites, the breach underscores the importance of making sure you don't reuse passwords across multiple accounts.

"The real issue now is that these passwords will be used to breach thousands of other websites unrelated to Yahoo, as cybercriminals use advanced automated tools to discover where users have used those same passwords on other sites," Shuman Ghosemajumder, chief technology officer of Shape Security, told NBC News.

Not all users took the threat too seriously, however.