Im not really sure why you think this is an exploit (versus some random guy with lot of votes and a lot of hash power)... this guy might just have gotten GPU mining to work or something, or just brought in a buttload of machines.

It does seem kind of weird that the miners in question keep changing their memo keys though. unlike many cryptos, miners don't get paid a ton here there might just not be that many people willing to invest in hardware to compete with him.

that said, id expect him to be slightly more subtle if he was a bad actor exploiting some kind of security hole, like not giving all his machines similar names.