In comic books, the idea of alternate realities is about as common as superheroes wearing capes. Most heroes at some point or another have experienced alternate realities. Whether they've journeyed there themselves or have come into contact with someone from one, there's a lot in the comic book worlds that are aware of their existence.
Even if the knowledge of their existence is limited, word is bound to get around to those with questionable motives. It would only be a matter of time before someone tried accessing alternate realities in order to gain information on others or situations that could be used to their advantage.
It could be argued that traveling to alternate realities isn't something just anyone can do, but over the years, we have seen several groups and individuals make the trip. Rather than try to gain wealth by stealing or taking over the world, what if individuals tried stealing secrets from alternate realities?== TEASER ==
The Watchers in the Marvel Universe are the biggest users of alternate realities. This powerful race of Peeping Toms knows all the secrets of the 616 universe as well as the infinite others. Uatu watches from his place up on the Moon and he doesn't exactly have the best security system.
We've seen certain individuals gain entry into his private residence and recently there were even a couple guys that took advantage of the fact that Watchers enter a fugue state every three years for exactly forty-five minutes. This gave them the opportunity to enter his place and observe a bunch of scenes from future and alternate realities.
One of the scenes they got a look at was a possible future scenario where the Ultron War was taking place. This scene involved Hawkeye and Spider-Man only Spider-Man had lost his mask (and most of his costume, as usual). These guys could have easily captured an image of Peter's face and while he might be one face in about eight million, that could be a valuable piece of information. There are clearly bigger secrets they could gain but selling an image of Spider-Man's true face or trying to blackmail him with it could be worth something.
What about when Barry Allen first met Jay Garrick? Once he realized he somehow journeyed from Central City to Keystone City, the home of a fictional character in a comic book he read about as a child. He immediately finds Jay's home and tells him he knows all about his origin and adventures. In a sense, it could be said that anyone in Barry's DC Universe knew all the secrets of Jay and the Justice Society.
There were crossovers from time to time between Earth-One and Earth-Two. The advantage could be used against them if their secrets and identities were known. Once Crisis on Infinite Earths merged the worlds, this wasn't as big of a concern but the decades of continuity before could have caused problems.
Then there were the Exiles in the Marvel Universe. A being calling himself the Timebroker enlisted heroes from different realities sent to specific ones to fix broken events. While on their missions, they became aware of many secrets of the different heroes and villains. Some had died or taken different paths in their lives based on whatever events transpired in their reality. Members of the Exiles were privy to this information along with any other that they came across.
When members were relieved of duty, they were thought to have been returned to their home dimension (but that's another story). In the end, it appears that members were allowed to come and go once the team moved away from the Timebroker.
Even Mister Fantastic used the idea of alternate realities when trying to solve everything. Building a device, he met the Council, consisting of different Reed Richards from alternate realities. All this turned a little sour as some evil Reed Richards made their way into the 616 Universe.
The idea of Nick Spencer's INFINITE VACATION even gives individuals the opportunity to visit other realities. If you have the money, you could buy an alternate reality and the secrets or information that go along with it. A lot of care needed to be taken to avoid getting stuck in an alternate reality.
Not just anyone can gain access to alternate resources. But once it's discovered that someone does have access or has had access to other dimensions, it's just a matter of force, threats or blackmail to get them to divulge secrets or a way to gain secrets. Supervillains need to forget robbing banks or trying to take over the country. If they can access the secrets of alternate realities, the world will be theirs for the taking.