From The Collaborative International Dictionary of English v.0.48 [gcide]:
Nana \Na"na\, n. [prob. from babytalk.]
Grandmother.
[PJC]
From Jargon File (4.4.4, 14 Aug 2003) [jargon]:
NANA
//
[Usenet] The newsgroups news.admin.net-abuse.*, devoted to fighting
spam and network abuse. Each individual newsgroup is often referred
to by adding a letter to NANA. For example, NANAU would refer to
news.admin.net-abuse.usenet.
When spam began to be a serious problem around 1995, and a loose
network of anti-spammers formed to combat it, spammers immediately
accused them of being the backbone cabal, or the Cabal reborn.
Though this was not true, spam-fighters ironically accepted the label
and the tag line "There is No Cabal" reappeared (later, and now
commonly, abbreviated to "TINC"). Nowadays "the Cabal" is generally
understood to refer to the NANA regulars.