Since the wiki is very low volume, there have been almost no changes over the past month, other than spam. The simplest method it would seem then would be to do a site roll-back for one month.
Is this possible?
Do you have backups? If so, just import an old backup. If not, maybe you can use the Nuke extension (http://www.mediawiki.org/wiki/Extension:Nuke). Others may have better options.
V/r,
Ryan Lane