Dash Core Group made an announcement on the several Dash wallet addresses comprised around 51% of all Dash mining hashrates.
According to the announcement, Dash Core Group was made aware of claims that several Dash wallet addresses comprised around 51% of all Dash mining hashrates. However, they don't believe the entity in control of the wallets in question plans or wants to attack because their mining activities began at least 4 months ago and their blocks have been published for all to see.
Additionally, because of their unique InstantSend capabilities, a transaction that was successfully locked via InstantSend would require a reorganization of over 24 blocks in order for a double-spend to succeed. Dash recently announced an innovation named ChainLocks that will make it even more difficult to perform a 51% percent attack on the Dash network since it would also require a 51% dominance of the masternode layer.