Ailing online firm Yahoo has warned Facebook it will take legal action against the firm if it does not sign licensing deals for patents it believes the social network is using for its advertising systems, according to reports.
"Yahoo has a responsibility to its shareholders, employees and other stakeholders to protect its intellectual property," Yahoo said in a statement according to various sources, including The New York Times.
"We must insist that Facebook either enter into a licensing agreement or we will be compelled to move forward unilaterally to protect our rights."
Facebook said it was not yet able to issue a full response to the claims as it was only just made aware of them.
"Yahoo contacted us at the same time they called The New York Times and so we haven't had the opportunity to fully evaluate their claims," it said.
The stance taken by Yahoo could open up yet another swathe of litigation in the technology sector, where numerous firms including Google, Apple and Microsoft are embroiled in patent battles as firms look to impinge on competitors' ability to operate effectively
Yahoo has struggled in recent years to capture its former success, with previous chief executive Carol Bartz fired by the board and replaced by ex-PayPal chief Scott Thompson, while founder Jerry Yang has also left the company.
Yahoo famously turned down a whopping $44bn deal for the firm from Microsoft in 2008, believing the amount did not represent the full value of the company.
Comcast's £29.7bn winning bid more than twice the £13.7bn Rupert Murdoch valued Sky at just eight years ago
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