PayPal suggests that generating a PIN by spelling words (on a numeric pad, e.g.,
[ABC] = 2) is a good method for security and memorability, e.g.,
B-L-U-E-C-O-W = 2583269.
My knowledge about password security is limited and I have not found any information about this. While these PINs are not completely random it seems to me that they should be (depending on words) quite secure†, at least for what PINs usually protect (just 4--8 numbers) and with other measures such limited attempts.
† I just realized that 0 and 1 are not mapped to letters, so those might have to be interspersed at random.
Can anything be said directly about the security of PINs that spell out words?
Has any research or attacks been made regarding these kinds of PINs?