The modern worker’s calendar was meant to be a ledger of obligations. It has become, like every door ever built, something that can be knocked on by strangers — and lately the strangers have learned to let themselves in.
When Pete Thomas, chief technology officer of the Los Angeles fintech firm Kapwork, spots a meeting he doesn’t remember scheduling, he begins what amounts to a small investigation: the sender’s name searched in his inbox, then LinkedIn, then a scan of the invitation itself for odd URLs and other red flags before he deletes. Several invitations in recent months have failed his checks. “It’s a distraction,” he told Business Insider. “You always have to look for context.”
The numbers climb
Whatever Thomas is seeing is not anecdote. Calendar-led attacks surged more than tenfold in August from July, according to a recent study from the email security firm Sublime, while a midyear Microsoft report found such attacks nearly quadrupled in June from May. Cybersecurity professionals say AI is making the schemes more convincing — and warn that AI agents, the obedient assistants now accepting invitations on workers’ behalf, could soon be opening the door themselves. “You suddenly have new and interesting opportunities because of these personal agents,” said Hugh Thompson, program chair of the RSAC cybersecurity conference and former chief technology officer of Symantec.
The anatomy of the scam, as the experts describe it, takes two forms. In one, the invitation itself carries the payload: a compromised meeting link, a credential-harvesting form, a prompt to download malware, said Ron Kerbs, CEO of Kidas, which builds tools to detect scams and deepfakes in voice calls. In the other, the victim joins what looks like a legitimate video call and finds an impersonator — someone using a real staffer’s name, a fake email address, perhaps AI-generated audio or video. “They’re using deepfake technology to look the same as the guy from IT,” Kerbs said.
Calendar invites make attractive vehicles, said Mark Beare, an executive at the cybersecurity firm Malwarebytes, because a meeting carries its own urgency — and because workers in sales, recruiting, consulting and other client-facing trades spend their days taking meetings with people they have never met. Microsoft adds a quieter technical reason: invitations are processed differently from email attachments, and malicious links can land on a calendar without the user ever explicitly opening anything.
Nine and a half out of ten
Aman Gairola, cofounder of the Indian design agency Say Design, thought he had landed a client in June when someone booked a meeting through his company’s website. The invitation held a link to what looked like a Google Drive folder with a project brief. He clicked, and the page that opened looked like Google Drive — but something felt wrong. He checked the URL, saw it was fake, and stopped before opening any files. “If I have to rate this, how convincing it is, I would rate it a 9.5 out of 10,” he said. Say Design is now considering dropping direct booking from its website in favor of a form. “It has definitely added a layer of scrutiny to the invites that we get.”
Sometimes the sender truly is someone you know. Scores of Jenn Drummond’s contacts recently received a calendar invitation from her email address warning that they had been served with a court summons; the linked fake legal notice asked for their financial information. Her account had been hacked while she was boarding a flight. Drummond, a world-record-setting mountaineer and keynote speaker, said that even if most recipients recognized the scam, she grieves what it did to her name. “What are people going to think? I’m not trustworthy — and your brand is what you build trust on,” she said. “I was sick to my stomach.”
The lock that cannot be picked
The professionals are blunt about the limits of vigilance. Mathew Woodyard, director of threat intelligence at the identity and access management company Okta, argues the burden belongs on the businesses that run the services. “The strongest mitigation isn’t user education about ‘spotting a fake invite,’ since the invites increasingly look identical to legitimate ones,” he said. “It’s giving users something that can’t be phished in the first place.”
That something is the passkey: a credential created for a specific page that works only on the authentic site, not on any convincing mock-up — removing the moment of human judgment the entire trade in deception depends on. “Until phishing-resistant factors like passkeys become the default rather than an opt-in afterthought, phishing attacks will keep working,” Woodyard said.
Until then, the calendar remains what every institution becomes when it is trusted by default: a road into the house, walked by anyone who learns the address.