Vandalism is a recurring problem for our community (and for others as well, of course!) and it's helpful to the admins if regular wiki contributors step in to clean some of it up. Although there are some things that only admins can do, such as deleting pages, a lot of problems can be fixed by "regular" people.
If you do clean up some damage, please do let an admin know. If nothing else, the admins may want to block the person who caused trouble from editing the wiki.
Thank you for your help!
The quick "undo"
If a page has been damaged, and nothing has been done to that page since, it's usually easy to undo the damage. If you click on one of the little "page" icons on the Special:WikiActivity page, you get to see the change that was made. The top part of that page shows the before-and-after parts of the change. Near the top of the right column, you'll see "(undo)". Click on that. Unless there's some complication, that will undo the change.
Undoing from a page's history
If changes have been made to a page since it was damaged, it may still be possible to reverse the damage. On the page near the top right is a box with a pencil icon and the word "EDIT". Beside that is a downward arrow for a drop-down menu. One of the items in that menu is "History". Click on that.
This will give you a page listing all of the changes that have been made. If necessary, you can see more changes than initially appeared -- you can specify a list of 20, 50, 100, 250, or 500 changes, and you can look at "newer" or "older" sets of changes.
Towards the left side of that page are columns of radio buttons. With these you can select two page versions. If you then click on the "Compare selected versions" button, you will be shown all of the differences between the versions. Again, near the top of the right column you will see "(undo)". Try clicking on that.
Whether this will work or not will depend on whether there have been other changes made to the affected parts of the page. It's worth a try.
Restoring an earlier version of a page
Or, "cleaning up a big mess".
From the page history, you can click on a time-and-date label, such as "16:07, July 11, 2017". This will show you that version of the page. At the top of that page, information is displayed giving the details: the time and date, and the account that made that change. Just below that are labels for:
- "(diff)", which shows the difference from the previous page version;
- "Older revision", which shows the previous page version;
- "Latest revision", which shows the current version of the page;
- "(diff)" which shows the differences between this version and the current version;
- "Newer revision", which shows the next page version;
- "(diff)", which shows the difference from the next page version
These, and the page history list, let you scan through the versions until you find out where the bad changes start. Go to the page right before those changes -- that is, the last "good" version of the page.
Then you click on the "EDIT" button near the top right.
The wiki will go into edit mode, and will show a warning: "You are editing an old version of this page. If you save it, any changes made since this version will be lost." Usually, that's a bad thing. In this case, it's exactly what you want. All you have to do is publish that page, with no further changes, and it's right back to that earlier version.
There's a catch, of course, if there have been "good" changes in the meantime. You would have to re-add those manually, which is usually kind of a pain.
A stitch in time...
Rather obviously, repairing damage is done most easily if it's caught early, before any more changes are made to the page. If you can spare a few minutes to deal with such things as soon as you see them, it can save someone a lot of time and trouble later.
Again, thanks very much for helping!