I just happened to catch /USR/SBIN/CRON in the output of ps, which strikes
me as suspicious because it's in all caps instead of all lowercase.
I ran strings over /usr/sbin/cron, and everything looks normal, but I'm
wondering whether this is something normal, part of a known rootkit's
signature, or something completely weird.

-- 
That's not gibberish...  It's Linux. - Byers, The Lone Gunmen
Geek Code 3.12:  GCS d? s+: a C++ UL++++$ P++>+++ L+++>++++ E- W--(++) N+
o+ !K w--- O M- V? PS+ PE Y+ PGP t 5++ X+ R++ tv+ b+ DI++++ D G e* h r y+