There was an interesting Imgur post about a number of historical battles, and one of the mentioned was the Battle of Mikatagahara. In the battle a ninja named Hattori Hanzō attacked in the dead of night and threw the enemy's vanguard into disarray. Upon reading further about Hanzō, though, it seems he is also regarded as being a samurai.
So here's my question:
Didn't samurai have a strict code of honor that a ninja's actions (like a sneak attack at night) would go against, thus preventing Hattori Hanzō from being both?