The first scam came knocking that same evening.
On Mio's screen, the machine kicked one up. A single entry in the new-account review queue, flagged as "not like the others." Her fingers stopped.
"Here it is."
Mikoshiba and Aya gathered around the desk. On the screen was one freshly registered account. The profile picture was a familiar face. An investor who was on TV all the time. Under a title borrowed from his name,
30% monthly returns. Principal guaranteed. Limited time only. Details here.
ran the account's first post.
"Is that a real person?" Aya frowned.
"The face is real. The words are lies." Mio's fingers moved. "Face matching says it isn't his official account. He never made this account. Unauthorized use. And—" She traced the text with a finger. "'Sure thing.' 'Guaranteed.' 'Limited time.' The hype trifecta. The landing domain was registered three days ago. Owner hidden. Built on the assumption it'll be short-lived and thrown away."
One weak clue, two, three. Mio checked each of them with her own eyes. The machine had only kicked it up as "one that's not like the others." The final call, black or white, was hers.
"Face unauthorized, words all hype, domain three days old," Mio said. "Every one of them has the face of a scam. I'm dropping it."
She struck the key. The account was quietly frozen without ever appearing in anyone else's feed. The engine she'd left behind on her old company's board was no longer in her hands. This was a half-built contraption she'd reassembled with the same instincts, its net still coarse. Even so—this time, on their own board, just before the tap, they had stopped the first lie.
"Well done," Mikoshiba said. "A memorable first catch."
Mio didn't take any pride in it.
"That one was easy to read, so I stopped it," she said flatly. "We don't have any samples of scams yet. So I kick up whatever's 'not like the others,' and I look at it myself and decide. It's a coarse net. Which means, conversely—it'll kick up real new users too, just for being unfamiliar. And we're the ones they'll come yelling at." Mikoshiba started to open his mouth, and Mio stopped him with a raised hand. "And the reverse is even more troublesome. If they show up with an ordinary face and slip in bit by bit, split across a bunch of entries—each one looks clean on its own. They won't catch in the net."
"Then make it stricter," Mikoshiba said. "Raise the threshold and drop anything suspicious. That'll cut down on what slips through."
"Picture an airport." Mio looked up from the screen. "You want to stop terrorism a hundred percent, so you raise the screening standard as high as it'll go. Nail clippers, water bottles, keychains—all confiscated. Everyone takes off their shoes, everyone gets a thorough pat-down. What do you think happens?"
"...The security line doesn't move."
"Every decent passenger misses their flight. The airport's in a panic. Same for us. Raise the threshold and scams go down. But real new users get kicked out as 'suspicious,' locked out, and come yelling at us. A hundred-percent safe airport is an airport nobody can fly out of."
"So, back to 'looks clean,'" Mikoshiba said, steering the conversation back. "If they slip in with an ordinary face, what then?"
"Machines can catch ninety percent." Mio nodded. "The remaining ten percent, a person has to look at. That's why I won't build it to reject everything automatically. Borderline cases go to human review, and those judgments get fed back to the machine to learn from. Ninety percent by machine, ten by people. Where you draw that line is the hardest part of the job."
"And people don't only look at the ten percent that gets kicked up," Mio went on. "Right now, everything I mark clean, I check with my own eyes before storing it as 'normal.' If I trained it without checking, then that one from before—the one that slipped in with an ordinary face—the machine would learn it as an 'example of normal.' The yardstick itself gets dirtied by scams. Besides, someday, to raise a machine that sorts legitimate users from scams, it'll need examples that say 'this is legitimate' too. So I store both. That's how the machine gets a little smarter at a time. For now there are few enough people that I can look at all of it. But—"
Mikoshiba watched her profile for a while. For one beat, his eyes dropped to the list piling up by her hands, waiting for review.
"I like that."
"Like what?"
"A company that says 'We have zero scams' flat out, versus a company that says 'We'll stop ninety percent, and people will check the other ten.' If I were a customer, I'd trust the second one." He turned back to the admin dashboard. "Honesty is the longest-lasting sales pitch there is. I'll remember that."
Mio didn't think too deeply about what he meant. To her, ninety-to-ten was a description of fact without exaggeration, neither a belief nor a sales pitch. Only the fact that Mikoshiba had taken it happily stayed at the edge of her vision.
When night came, the first report arrived.
It wasn't a scam. It was from one of the users—an elderly woman with a photo of her grandchild on her profile. In the free-text field of the report form, she had written one short line.
"I'm so glad I found a place where my family can look at my grandchild's photos without worrying. Thank you."
"...So there are people who write 'thank you' in a report form," Mio said, a little surprised. "I hadn't anticipated that."
Mikoshiba looked at that one line for a long time. Some of the usual cool composure of a salesman had drained, just slightly, from his face.
"This is it," he said quietly. "This is what I started the company for."
Mio, as expected, felt no resonance with that dream. What drew her wasn't the flag but the board you planted the flag on. That hadn't moved a millimeter since the day they founded the company.
Still, her interest lingered on the single point that the "thank you" had been unanticipated, and then moved quickly on to the next number. A user's gratitude, too, was just one more piece of observed data to her. From an unusual distribution.
"Himuro." Mikoshiba set coffee in a paper cup by her hand. "A hundred people. Your engine protected the first hundred."
"A hundred," Mio said, taking a sip of the coffee. "As people increase, reports increase. Complaints about false positives increase. It means my work increases."
"That's right," Mikoshiba laughed. "As people increase, there's more to protect. That's what it means for a company to start running."
Aya pointed to a small number in the corner of the admin dashboard. Active users: ninety-eight.
"Two more and it's a hundred."
That night, Makoto's user count reached a hundred and one.
On her way out, Mio scrolled through the detection log one more time.
The first impersonation account she'd dropped. The landing domain of the external link on its profile had been a throwaway that would vanish in three days. But Mio felt a small sense of something off in a corner of the log. After it had been dropped—as if checking "why it had been dropped"—a very similar new account, its text changed only slightly, had appeared once more.
She'd dropped it right away. 0.91. No problem.
Still, it was the faint sound of footsteps that said "they're thinking about how to slip through, too." Mio didn't call it footsteps yet. On a board of a hundred and one people, there was noise beyond counting.
She closed her laptop, already thinking about the next problem.