Remember, if you use vBulletin for your own forums, you may have joined theirs at some point in the distant past. If you are a member of a forum that uses vBulletin (No we don't) the owner of the site or head of the clan may also have joined their forum. Please inform them.
For the moment mostly only people with an account at vBulletin have to worry. vBulletin did issue updates for the affected versions within hours. Thankfully some newer systems are a cloud service, so their update is done. If you use a site that uses vBulletin, do what I did and inform the admin.
The links below are the first report, and the resulting extended implications.