Google has issued a lawsuit against BT in both the US and the UK over what it claims is an infringement of its patents.
In 2011, BT launched its own legal action against Google for infringing six of its patents in a US court in Delaware. The case is yet to be resolved.
In retaliation, Google has said that it is taking action against BT by filing infringement on four of its patents "as a last resort", adding that the firm "works hard to avoid lawsuits".
It went on to say: "BT has brought several meritless patent claims against Google and our customers, and they've also been arming patent trolls. When faced with these kind of actions, we will defend ourselves".
BT said that its policy was not to comment on pending litigation and could therefore not provide any further information on the matter. Details on the action taken against BT in the UK are still unknown at this point.
The complaint in the US, which was filed on Wednesday in California, saw Google file for four patent infringements. Two of the patents, 5,581,703 and 5,701,465 are for "a method and apparatus for reserving system resources to assure quality of service". Patent 7,460,558 is for a system and method for data prioritisation in a multi-tier network system. These three patents were initially assigned to IBM but are now owned by the search firm.
Finally, patent 6,807,166 is for a gateway for internet telephone systems, which manages calls to and from PCs with either a private IP address or one assigned by a DHCP server. The patent was originally filed by Fujitsu in 1999.
In a blog, patent consultant Florian Mueller said that since Google has complained about BT "arming patent trolls" it would have been more appropriate for Google to sue BT or have third parties sue BT over home-grown Google patents. Instead, however, the search firm is pressing ahead with patents formerly belonging to IBM and Fujtisu.
"Google's statement does not explain why it's fine for IBM and Fujitsu to arm Google but unacceptable that BT sells some of its intellectual property to third parties," Mueller said.
He went on to add that while Google's dominant position in the US could work in its favour, in the UK things may not be as clear cut.
"The UK is a jurisdiction in which patent holders rarely win, and if they win at all, it's not a country where you have juries that render billion-dollar damages verdicts," said Mueller.