Okay, time for a quick recap. First off, you may recall that last month Yahoo sued Facebook over patent infringement, citing 10 Yahoo patents Zuckerberg's social network had allegedly infringed.
Just over a week later, Facebook snapped up 750 patents from IBM to bolster its war chest, a major addition as the social network only held 56 issued patents (and 500 filed) as it was.
So, bet you can't guess what's coming next. Yes, as all good tech companies do, Facebook has responded by counter-suing Yahoo over patent infringements. Exactly 10 patents are cited in the counter-suit, mirroring Yahoo's original volley of legal fire.
Facebook's allegations of patent violations pertain to advertising, privacy and photo sharing among other issues.
Ted Ullyot, general counsel at Facebook, commented: "From the outset, we said we would defend ourselves vigorously against Yahoo's lawsuit. While we are asserting patent claims of our own, we do so in response to Yahoo's short-sighted decision to attack one of its partners and prioritize litigation over innovation."
Which roughly translates as "they started it" - although in fairness, that is true.
Yahoo's response was: "We have only just received Facebook's answer and counterclaims, but on their face we believe they are without merit and nothing more than a cynical attempt to distract from the weakness of its defense."
We doubt it's last orders at the social network patent infringement bar yet, and we expect the next round will come courtesy of Yahoo.