The Meme was a psychic worm made by Jack Harkness from the ruins of the intelligence of the Cardiff Bay Intelligent Hotel and Spa. His plan was to use it to encourage people to feel thoughts of rebellion so as to destabilise the Sorvix rule.
However, Red Doors further engineered it and made it into a weapon to drive people to violence. It existed in the internet and sent cards to people through which it could use its power, encouraging Serena to kill Michael Hughes among many other things. Yvonne Hartman was able to draw it into her blood by proving resistant to a card, allowing St John Colchester to get a full psychic signature and set about tracking it down. (AUDIO: Tagged)