Horcrux #1 Destroyed: Diary

[Cindy]

No: HPFGUIDX 133724

COS pg 310
"I grew powerful, far more powerful than little Miss Weasley. Powerful 
enough to start feeding Miss Weasley a few of my secrets, to start 
pouring a little of my soul back into her..."

Oi! 

Obviously, the diary was given to Lucius Malfoy by LV before he showed 
up in Godric's Hollow.  What connection does the diary have to the 
other known and speculated horcruxes? Could only the fang of a 
Basilisk fang destroy the diary? Why wasn't the diary as protected as 
the locket?