Long before secret-sharing apps like Secret, Whisper, and Yik Yak were raking in millions in venture funding, Frank Warren was asking strangers to write their most closely-held confessions on a postcard and send it to his house. His project, called PostSecret, took off in 2005, and his digital chronicle of people’s secrets became one of the Internet’s most popular blogs. The New York Times called it the “PostSecret phenomenon,” and the project spawned multiple books, live events, art exhibits, and hundreds of thousands of scrawled revelations on the backs of postcards.

In 2011, Warren even had a PostSecret mobile app—not unlike those on the market today—until an outpouring of user-generated obscenity prompted him to shut it down. Where Warren demurred, others have soldiered on, and today anonymous communication services have become, to the surprise of many, big business. In July, the app Secret, popular within the San Francisco tech community, announced $25 million in new funding at a $100 million valuation. Its larger competitor, Whisper, has raised some $60 million to date.

Fortune called Warren to get his take on the next generation of secret sharing. He’s less than enthused. Secret sharers who use today’s apps can make themselves vulnerable, he says, pointing to lingering criticism about bullying and abuse. He also thinks that the latest platforms look an awful lot like his original app.

In the interview, Warren fingers the makers of Whisper, though he stops short of accusing them of sabotaging and copying the original PostSecret app. Still, he’s not exactly ruling out foul play. (In a statement, Whisper flatly denied the allegations and called the comments “disappointing because we are big fans of Frank and his mission, and in fact have reached out to him numerous times.”)

He also discusses the evolution of anonymous sharing and why people can’t get enough secrets. The interview has been edited and condensed for clarity.

You are the arguably the progenitor of anonymous secret sharing. How do these new apps complement the PostSecret legacy?

One thing that some people will say is that these new apps are based on the old PostSecret project, or this is an update of the original PostSecret, or we’re moving form the analog world of postcards to the more digital world of secrets. But what they’re missing is that PostSecret was the original secret app. We came out with the PostSecret app in 2011. It was the top-selling app in the U.S. and Canada, but it was only around for three months.

Why just three months?

It was an internal decision. We felt that it was no longer a safe place to share secrets.

Why was that? What happened?

I guess it depends on how deep you want to go. It turned out that there was a very small but dedicated group of abusers of the PostSecret app. They were griefers determined to post malicious or sexual or bullying content in response to other secrets. It was cruel, and it made it virtually impossible to monitor because there were tens of thousands of secrets being shared every day.

It sounds maybe not so dissimilar from some of the malicious comments and inaccurate rumors that have been floated on these other apps. But they kind of stuck around, and are plowing ahead regardless.

Are they dealing with the same problems you saw, or do you think those apps fundamentally different than what PostSecret’s app was?

Well, PostSecret has been around for 10 years and it has a tradition of being community-oriented. It has a certain set of values and part of that is not exploiting people’s secrets for commercial reasons. So because of that, even though the website has had over 600 million visits, I’ve never taken one dollar for a paid advertisement. And so I think that’s the kind of environment that allowed people to really trust me with secrets they wouldn’t share with anyone else.

It was a safe place. It was a non-commercial place. That got infused in the DNA of the project, and so that tradition when we created the app the app also had, kind of, the spirit of that project. It had a soul. This culture that was already there, and maybe if it hadn’t been for kind of outside parties acting maliciously, we could have gotten to a place where we could have taken flight, gotten the wheels up.

A postcard on PostSecret.

I’m curious: looking at how commercially well some of these apps are doing—raising millions in venture funding—are you sort of wistful? Do you think that that should have been the PostSecret app, which was the original here? Or do you think it’s a different mission entirely?

I really don’t feel that wistful. I travel around for PostSecret events, and hear secrets shared live for audience members, sometimes thousands of people, and the PostSecret play in Charlotte, North Carolina ran earlier this year and is coming to New York and Vancouver. I’m doing what I want to be doing, how I want to be doing it. The spirit of the project continues to grow and spread. The only regret I do have is that I feel like in some ways PostSecret established this safe place to share secrets, and now there are other players who might not have the same intention, and young people especially are sharing and making themselves vulnerable in a way that might not be healthy, and that concerns me.

What are the problems with the other anonymous apps?

If you read the terms and you look at the technology, some of what they’re claiming is anonymity isn’t anonymous at all. I’ll give you one example. In the PostSecret app we put a lot of engineering into kind of hacking into the photos that were used, because every photo that you take with your smart phone has a digital fingerprint to it. So if you wanted to identify where a picture was coming from it’s possible, based on the digital signature of the photo. We went in and hacked that so that all the pictures were actually anonymous—there was no way to trace them back. Other apps that claimed to be anonymous, I’m not sure they’re all doing that.

There’s also information, again, in the fine print of these apps, that doesn’t necessarily back up their claims about anonymity. So that’s alarming. People might be posting these lurid things, and it’s not really that hard to figure out who they are.

But my biggest concern goes beyond that. On Whisper, people are able to identify secrets being shared that are in their community—near them. They can see where, generally, the secrets are coming from. And then they can reach out and text or communicate with that person privately. With so many teens on the app, and so many users who are emotionally vulnerable, that’s something that could attract the interests of sexual predators.

If you do some research online you’ll be able to identify crime reports of sexual predators who have used the Whisper app to contact young boys and women. One girl was 12 years old and a sexual predator contacted her in using Whisper and they communicated privately. He contacted her on the app, he went to her house I think, asked her to sneak out her bedroom window, and he took her to a hotel and sexually assaulted her. That’s a criminal case pending, and there’s another one that just came out a couple days ago. What does concern me is what this app make possible for very sophisticated sexual predators.

(Editor’s note: A Whisper spokeswoman responded to Warren’s criticisms with the following: “From day one, our number one priority has been maintaining the safety of the Whisper community. We have numerous technical safeguards, automated image and text analysis and user reputation review, in addition to having a moderation team of more than 130 people who enforce our guidelines.”)

A post on Secret.

That’s a strong critique. When these founders were setting up these other apps, did any of them contact you for advice at all? Have you spoken with any of them?

Some have reached out to me, yes.

What did you tell them?

My feelings of engaging with them are a little mixed, just because of the history.

The history of your app?

Well, I’ll share something with you. The biggest set of violators on the PostSecret app were people using TigerText. And we know this because of the secrets they would post linking back to TigerText, or saying “DM me on TigerText.”

Could you explain what TigerText is?

It’s an anonymous messaging app. And if you look into it, you’ll discover that the person there is now the person who is running Whisper. [That’s Michael Heyward, co-founder and CEO of WhisperText, Whisper’s parent company. —Ed.]

Of the secrets that were being shared on the PostSecret app, the biggest group that was in violation [of terms of service barring abusive activity] were people that were using TigerText. They were posting just the worst kind of content you can imagine.

Do you think that activity carries through to Whisper?

I don’t think Whisper has to worry about [abusive users from] TigerText.

What do you mean?

Some of the people using the [Whisper] app contacted me. They were upset because in some ways they felt like the same person who was kind of running TigerText in some ways might have been responsible for the downfall of the PostSecret app.There’s no evidence for this. But to pretty much create another app that’s ninety to ninety-five percent the same as the PostSecret app? And get, I don’t know, some people say $60 million dollars in venture funding? It had some people upset. It was difficult for me to hear those stories.

In what ways do you think it was TigerText that hurt the PostSecret app?

Let me bring up some of these posts [from the PostSecret app]. “PostSecret needs a [TigerText] filter so that people can search on that app and not here. Leave PostSecret alone.” “Absolutely despise TigerText, it’s ruining PostSecret.” “Hi, no one wants to TigerText you. If you want to show off your scary looking dick download Blendr.” “Dear Frank, can you please block the phrase TigerText? Please please.”

Did the founder ever reach out to you?

Michael Heyward? He’s contacted me before, yes.

Did you respond?

I responded, yes.

I take it you didn’t give him any business tips.

No. We didn’t have that kind of communication.

A post on Whisper.

Did he say anything about problems with TigerText users? Did you talk to him about this?

No, I have not talked to him about this and I have no evidence that he was personally involved in trying to bring down the PostSecret app so that there was space for Whisper. But others have shared their concerns of that with me.

What did you tell him?

I’ll keep that private.

(Editor’s note: A Whisper spokeswoman responded: “There is no connection [between TigerText, PostSecret, and Whisper] and these comments are disappointing because we are big fans of Frank and his mission, and in fact have reached out to him numerous times. Whisper was created with the mission of helping users find meaningful connections and support. We also have a non profit organization, Your Voice, with the primary goal being to reduce stigma around mental health for young adults.”

OK, outside of the app, what else is PostSecret doing these days?

Thanks for asking. There’s a new PostSecret book coming out later this year. There’s going to be a new digital companion that goes along with that book that’s being created by Potion [a design and technology firm]. We’re really excited about the possibilities there. We’re going to be able to take people into PostSecret headquarters and show them the pyramid of postcards, and we’re thinking about turning the project over temporarily over to a fan.

I continue to travel and have live PostSecret events. I just got back from trips to North Carolina; North Dakota; Barrie, Ontario—so that’s really exciting for me. And then the PostSecret play. Plus, a PostSecret spoken secret album will be released later this year.

A letter on PostSecret.

Do you think putting anonymous secrets online has a chance at being an artistic exercise? Or does Internet anonymity always sort of tend toward the obscene?

No, not at all. I don’t think volume is an indicator [of lacking quality]. I actually think the space has wonderful potential. I’d be really excited if we saw the right kind of architecture for true anonymity, in a way that could reflect back the full spectrum of our shared humanity.

One of the things I’ve discovered through PostSecret is that when you keep a secret, it feels like this wall that divides us from others. But that’s just an illusion. If we can find the courage and the vulnerability to share our secrets in the right ways with the right people, we can discover that these walls are actually bridges that don’t just connect us with others but with our true selves.

That’s enough to make me want to send in some postcards.

Oh you’re kind. This project, it kind of has a soul to it.