u/markort147

If the opponent plays [[Siphon Insight]], you are not supposed to know what cards are exiled face down. Untapped, instead, shows what cards are missing in the real-time decklist.

This is cheating.

EDIT:

1. As someone correctly said in the comments, if the problem is real, it is with WotC, because the info would be public and readable from the logs. Even if Untapped adds a filter, anyone else could develop another layer to cheat the same way. Thank you for pointing it out.
2. According to many, this does not happen. So I will check more accurately next time someone plays a similar card and I'll let you know.