I'm looking for security screw 3 open slots who knows what it is called, and what type of screwdriver u need?

Answer 1

Sounds like a tri-groove or tri-wing screw (no joke).

McMaster Car sells various security screws and has a decent selection of different types. Do a search on there site for "Security Screw".

For a McMaster part number of a tri groove screw look up P/N 90058A542

A tri wing bit is P/N 53265A311

Answer 2

I believe you are refering to a "Tri-Wing" type screw or bit.

Wiha makes a nice tri-wing bit set for any hex-shaft tool:
http://www.wihatools.com/indexes/indx_specialbits.htm
http://www.wihatools.com/719triwing.htm