Space.com has the story Has Dark Matter Finally Been Found? Big News Coming Soon.
Some physics theories suggest that dark matter is made of WIMPS (weakly interacting massive particles), a class of particles that are their own antimatter partner particles. When matter and antimatter partners meet, they annihilate each other, so if two WIMPs collided, they would be destroyed, releasing a pair of daughter particles — an electron and its antimatter counterpart, the positron, in the process.