lucy24 - 4:42 am on Dec 16, 2013 (gmt 0)
If this is in fact the robot responsible for the Google Plus list of icons, I can only say that they're pushing the idea of "I'm not a robot so I don't have to heed robots.txt" to the absolute limit. It's not as if people visit your profile page and explicitly click on something that says "Yes, please, show me the icons for these sites!"
But it's more principle than real injury. I'm not a front-driven site, so I generally don't even care if a robot stops by for an unauthorized pickup. And the favicon is exempt from all 403 blocks.