Not everyone realises how stupid they are.

• 404: That's 404-tan, a quasi-OS-tan who represents the standard http error code, 404, which means Not Found. She's from 2chan originally, as are all the OS-tans, but has bounced around the Internet for a while.
• 403: Mahoro, she's the target of an Internet meme, her chibi image is used in a sign saying, "Don't stick it in her pooper." Now, this image of forboding prompted me to seek out a better version of that image, in the end I found a source for what you see on error 403, it took some photoshopping, but was not hard and did not take long to make.
• 401: I really don't know her name, but she comes from an image called thanatos5ja.jpg, which has been around for a while on the Nets and finally came to my attention through #btc on irc.sorcery.net, I made the animated gif myself, and added the eyes and mouth, to make it conform to the lazer meme that exists.