NetBSD still used the 'old' BSD license, which included the (in)famous advertising clause. The advertising clause has been the subject of much debate and frustration, and as such, it was removed from the BSD license in 1999. The original clause read:
* 3. All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
* This product includes software developed by the University of
* California, Berkeley and its contributors.
The reasons presented by the NetBSD Foundation to switch to the 'new' BSD license stem solely from the same kind of issues that prompted the clause's removal in 1999: organisations and people were concerned about the clause, to the extent where NetBSD could not be used in commercial products. In addition, the clause was already ignored anyway by some people. "The members of the NetBSD Foundation (i.e. its developers) no longer [consider] clause 4 to be useful in today's software world."
All the code which was contributed to the NetBSD Foundation has been modified to use the new 2-clause NetBSD license, and the Foundation encourages people to use this license when assigning code to the NetBSD Foundation.