On 13 March 2015, 19:55:59 UTC, PrimeGrid’s 321 Prime Search project found the mega prime:
The prime is 3,531,640 digits long and enters Chris Caldwell's The Largest Known Primes Database ranked 12th overall. This is the largest known 321 mega prime and the largest prime found to date at PrimeGrid!
The discovery was made by Karsten Klopffleisch (KarstenK) of Germany using an Intel(R) Core(TM) i7-2600K CPU @ 3.40GHz with 16 GB RAM running Linux. This computer took about 18 hours and 33 minutes to complete the primality test using LLR.
The prime was verified on 18 March 2015 18:17:44 UTC, by Thomas Gbenro (dagee) of Germany using an Intel(R) Core(TM) i5-2500 CPU @ 3.30GHz with 4 GB RAM running Microsoft Windows 7 Enterprise. This computer took about 12 hours and 16 minutes to complete the primality test using LLR. Thomas is a member of the BOINC@Frankfurt Team.
For more details, please see the official announcement.