[Andreas]

Suggestion:

1. If it's a plugin only modification and the vulnerbilitie lies in the code or added templates, advise users to disable it
2. If it's a vulnerbilitie in a template modification that would still exist if all plugins are disable, advise users to revert the template(s)
3. If the vulnerbilitie lies in added files, advise users to disable the modification and delete all files added by the modification
4. If the vulnerbilitie lies in code added/modified in vBulletin files, advise users to overwrite files with the original ones

This way, it should be possible to protect users whil keeping them from loosing data.
Though, this provides more information about the type of vulnerbilitie - information that could be abused for searching the vulnerbilitie and exploiting it.