Just found this on 2 sites (on a server with maybe 8 installs, and it is godaddy host if that matters).
Domain A, 3 php files found in WP-ADMIN
class-dierdre-gregory.php
class-ftp-vivian-cry.php
theme-sybyl-agree.php
Domain B, 1 php file found in WP-ADMIN/IMAGES
arrows-babb-gateau.php
Both sites have a google cache from Dec 6th and were clean, nothing was added/removed to these sites EXCEPT the 3.5 WP update this week.
Removed said php files, and input added to header, now to go do a full clean and search.