Peoople have a maximum size and of course there are other claims so this should not be possible to claim.
but a player typed
/ps expand 10 10 10000 10000 10000 10000

caused server crash because I guess trying to open and load chunks
Server could not restart (too laggy to log in)
Fix : delete the claim in MySQL

Should not happen unless they have bypass permissions or OP, at which point all is fair game. There are legitimate uses for fields that large. Did they have bypass perms or OP?