Have a quick read through the posts linked in the article this story points to. I show that using just a UDID, you could access the user's geolocation, games they played, private messages and friends lists on many of the affected social networks, and in some cases (which affected millions of users) completely take over Twitter and Facebook accounts. This is with _just_ a UDID. Some of the companies I notified a year ago are still vulnerable today. And remember, I only looked at social gaming networks - small slice of the app ecosystem. I know that there are similar systemic issues in many other places. So yes, this is definitely a catastrophe.
Unfortunately, there's just not much an ordinary user can do. There's no way for a user to tell if an app accesses and broadcasts their UDID (if you're an expert you can use mitmproxy or a similar tool), and certainly no way to tell if the UDID is being used safely. I would recommend de-linking your social media accounts from all apps unless you know they're safe, but that's the kind of drastic advice that people tend not to take.
Unfortunately, there's just not much an ordinary user can do. There's no way for a user to tell if an app accesses and broadcasts their UDID (if you're an expert you can use mitmproxy or a similar tool), and certainly no way to tell if the UDID is being used safely. I would recommend de-linking your social media accounts from all apps unless you know they're safe, but that's the kind of drastic advice that people tend not to take.