The new gTLDs that are being implemented have a few security concerns already. One of the major concerns is Name Collision, which results from a single domain name being used in different places.
An example of this would be a company that uses .corp in an internal domain name. Under the new gTLD processes, the .corp gTLD could be bought by a different company for their use on the internet. If that happens, when a user tries to go to internal locations on a company network using .corp, there is a chance that they could actually get data back from the now legitimate .corp servers on the Internet.
Using an internal domain name like this is a very common practice among businesses, so any issues that may come up dealing with .corp could be widespread. In the case of these new gTLD's, the owners of those servers could also manipulate their records, redirecting wayward queries. This opens the door to possible malware or phishing attacks on unsuspecting systems.
via New gTLD security implications.