Thread:Project:Support desk/Massive spam & vandalism. more than 150.000users!/reply (15)

Agreed with 88.130. Restoring a backup without finding and fixing the security hole will give you the same problems again.

Just a note: you can export specific pages from the wiki before restoring the backup to import them when restoring so you don't lose the work. See the Special:Export page on your wiki and Special:Import.