When viewing [[Special:BlockList]] you can see information that has been RevDeleted.
Example:
http://www.mediawiki.org/wiki/Special:BlockList => "11:35, 13 October 2010, Jyothis (Talk | contribs | block) blocked Yourmomsuckscock (Talk | contribs) (infinite, account creation blocked, e-mail blocked) (crosswiki abuse<!--globally locked; about bot-->) (unblock | change block)"
That block log (The username only) was revdeleted so it was hidden, see http://www.mediawiki.org/w/index.php?title=Special%3ALog&type=&user=&page=User%3AYourmomsuckscock&year=&month=-1&tagfilter=&hide_patrol_log=1&hide_review_log=1
Version: 1.20.x
Severity: major