First, I said that Googling "unadvisably" - AKA the Adverb From Hell (AFH) - brought up a host of hits from a bunch of eminent authors and publications, from Milton to the present day. And indeed it does - with over six hundred citations in the Google Books corpus alone (to give you an idea of how conclusive that is, that’s twenty times as many citations as come up for its first cousin "ill-judgedly", a word that Fay Weldon has used in print without anyone accusing her of not knowing bad writing from good).
Second, I said that the AFH was in The Concise Oxford Dictionary. And indeed it is — or rather "unadvisable" and "advisably" are, but with this note in the "Using this Dictionary" section:
The inflection of nouns, verbs, adjectives and adverbs is given when it is irregular, or when, though regular, it causes difficulty
That, in case it needs spelling out (and in this case I fear it probably does), means that an adverb won't be included if it’s regular, as the AFH is, and causes no difficulties, as the AFH doesn't - or at least managed not to for several hundred years until they started braying "It's not a word!" at it on the Internet.
I can't even remember why I used the AFH in the first place. It's certainly not a word I bandy about in my everyday conversation. I assume I may have wanted to avoid using another adjective beginning with an "i" in the sentence it appeared in, or something subconsciously style-driven of a similar sort. Hell, it may even have been a typo, and I let it stand because I knew full well that, while not particularly common, it's a perfectly kosher word - as Google Books and dictionaries then more than confirmed.
So there we have it. More lies than you can shake your dic at. Six hundred and eight of them, in fact.
To paraphrase the bloke who inadvertently started this whole surreal and sorry saga: fuck off, middlerabbit.