Fake Calendar Invites Now Land Before You Click

Fake calendar invites rose 1,216% in August, according to email security firm Sublime Security, and many never need a click to appear. Google Calendar can drop those events onto a work grid on its own, sitting beside real 1:1s and client calls.

Microsoft Threat Intelligence recorded the same shift in June, when calendar invitation files nearly quadrupled, up 277%. Workers who live on stranger meetings, in sales, recruiting, and consulting, are first in line.

A Meeting Nobody Booked

Pete Thomas, CTO of Los Angeles fintech firm Kapwork, treats an unfamiliar slot as a mini investigation. He searches his inbox for the sender, then LinkedIn, then scans the invite for odd URLs before he hits delete. He has received several that failed those checks. “It’s a distraction,” Thomas said. “You always have to look for context.”

The calendar is doing part of the attacker’s work. Google Calendar users get three choices for inbound events, and the open choice writes a meeting onto the grid with no accept click. Work and school accounts do not always control that choice themselves. If an option is greyed out, an administrator has already limited it.

HOW GOOGLE ADDS INVITES

• From everyone: All invitations sent to the user’s address are added to the calendar on their own.
• Only if the sender is known: Events auto-add when the sender is in Contacts, in the organization, or someone the user already messaged.
• When I respond in email: The event appears only after the user answers the invitation message.

Google’s own help page tells people they can add invitations from known senders only, and it warns that the known-sender choice can reveal to a sender that they are not in Contacts. Updated settings apply to new invitations. Events already on the grid stay put until someone deletes them. Marking a sender as known, or even sending them one email, can open the door to later invites from that address, which is why a hacked mailbox of a real contact is so useful.

Luke Wescott, a threat detection engineer at Sublime, put the social piece simply: a junk mail from a name you do not recognize is easy to ignore, and the same lure beside a dentist visit or a weekly meeting with a boss borrows that slot’s credibility. “Calendar apps, such as Google Calendar, can add invitations automatically without users even accepting them,” Wescott said. “So scammers don’t even need you to open an email.”

1,216% in a Single Month

Sublime’s detection team had watched ICS phishing, the trade name for malicious.ics calendar files, climb through 2025. The 1,216% jump in August over July is the month it treated as the move into the mainstream. Mark Morris, who wrote up the samples for Sublime, listed free Gmail accounts, Google Calendar, and Microsoft systems as the usual pipes, with Google first.

CALENDAR ATTACKS SUBLIME COUNTED

Microsoft’s Q2 2026 email threat note, published July 23, measured a narrower slice: ICS files were still about 4% of malicious payload volume, and they still calendar invitations processed differently from ordinary attachments. That difference is the whole trick. A meeting request can inject a link onto the calendar without an open-and-click on a file. Microsoft said those ICS payloads nearly quadrupled in June, up 277%.

Between June 14 and 15, Microsoft Defender Research watched a separate multi-stage campaign that mixed a nested EML, framed as a Teams recording, with an ICS invite aimed at placeholder admin addresses. It reached more than 107,000 users across nearly 19,000 organizations, almost all in the United States, with financial services at 17% of the mix, technology and software at 14%, and retail and consumer goods at 14%.

Sales Teams Invite the Strangers In

Open booking was supposed to take friction out of intro calls. It also hands a stranger a legitimate path onto the calendar. Aman Gairola, cofounder of Indian design agency Say Design, thought he had a client in June when someone booked through the company site. The invite pointed at what looked like a Google Drive folder with a project brief. He clicked, landed on a Drive look-alike, checked the URL, and stopped before opening files. Say Design is weighing a switch from direct booking to a form.

If I have to rate this, how convincing it is, I would rate it a 9.5 out of 10.

Aman Gairola, cofounder, Say Design

Mark Beare, an executive at cybersecurity firm Malwarebytes, said the invite creates urgency, and that office workers are used to meetings from colleagues, clients, and partners. Ron Kerbs, CEO of Kidas, which builds tools to spot scams and deepfakes on voice calls, splits most jobs into two shapes. One plants a bad meeting link or a form that asks for logins or a file download. The other gets the target onto a video call with someone using a real staffer’s name, a fake address, and AI audio or video. “They’re using deepfake technology to look the same as the guy from IT,” Kerbs said.

Fortra has been tracking a third path that exploits the handoff inside a company. Attackers pose as a prospective customer to a non-sales employee, ask to be pointed at sales, and send a booking link to forward. Sales gets a note from a colleague, picks a slot, and hits a Microsoft 365 sign-in framed as a step to sync the booking. Fortra’s line on why it works is the chain itself: external sender, helpful employee, internal forward, sales recipient, booking page, sign-in prompt. Every step looks ordinary, so the full path does not feel like phishing.

Hugh Thompson, program chair of the RSAC conference and a former chief technology officer of Symantec, is already looking at the next handoff, when a personal agent is the one holding the calendar. “You suddenly have new and interesting opportunities because of these personal agents,” Thompson said. The public argument on X has been less about those agents and more about a simpler fact: people who live on booking links already treat a new slot as routine until it is not.

Why Fake Meetings Survive a Spam Filter?

Morris’s write-up is blunt about the gap. Meeting invitations go to the inbox and the calendar at once. Most email tools are built to stop the first copy. Email and calendar also run on different protocols, so a quarantine can still leave the event on the grid with its link one click away. Security teams that only empty spam folders are cleaning half the attack.

The other half rides trusted pipes. Sublime’s recent RMM sample arrived from a Gmail address, which is a poor denylist target, as a Google Calendar invite, which most mail filters do not triage as a calendar object. Google Calendar then rewrote the payload URL so the first hop a scanner sees is google.com, even though the real destination was a free Framer page pushing a fake credit note for $1,109.08. In looser Microsoft setups, that click downloaded a roughly 10MB ScreenConnect.ClientSetup.msi, a real remote-management installer pointed at the attacker’s tenant.

Wescott’s working list of titles is mundane on purpose, which is why they survive a glance on a busy Tuesday.

COMMON CALENDAR LURES

• Voicemail bait: Titles such as New voicemail received push a callback or a file.
• Fake receipt: Payment receipt confirmation, $298.99, is the kind of dollar figure Wescott keeps seeing.
• PayPal warning: PayPal unusual activity copy tries to force a same-day login.
• Auto-pay clock: Your auto-payment will be processed within 24 hours is the urgency version of the same trick.
• Contract bid: An invitation to bid on a contract is aimed at people who actually want stranger meetings.

Canada’s anti-fraud centre flagged the consumer version of that receipt bait on May 5, 2026, describing invoice and subscription notices in the name of firms such as PayPal or Norton that trigger a calendar event, often added on its own, then a Join meeting or View details link to a fake login page.

🚨 Fraud Alert: Calendar Phishing

Fraudsters are sending emails that look like invoices or subscription notices from companies such as PayPal or Norton. These emails include or trigger a calendar invite, that are often automatically added to your device calendar.

How it works:… pic.twitter.com/sGSh2uJD8p

— Canadian Anti-Fraud Centre (@canantifraud) May 5, 2026

Wescott’s other practical rule is easy to miss. Do not hit decline on a suspicious invite, because that reply can tell the sender the address is live. Delete the event, and report the message as spam if the mail host offers it.

When the Sender Is Someone You Know

Sometimes the From line is honest, which is worse. Scores of contacts of Jenn Drummond, a world-record mountaineer and keynote speaker, got an unexpected calendar invitation from her address warning that they had been served with a court summons. The invite went out after her email was hacked while she was boarding a flight, and it linked to a fake legal notice that asked for financial information.

Drummond said she felt sick, even if most recipients spotted the scam, because some people might think she was suing them, or that she had been hacked. “What are people going to think? I’m not trustworthy,” she said, adding that a brand is what you build trust on.

A compromised mailbox does two jobs at once. It inherits whatever trust the owner already had, and under Google’s known-sender rule it can keep auto-adding events to anyone who had already exchanged mail with that account. Tightening the calendar to known senders still helps against cold Gmail blasts. It does not help as much once a real client, a recruiter, or a colleague is the sender.

Google Left the Calendar Door Unlocked

Google already offered those three invitation choices to users. Until mid-August, Workspace admins could only set the default for new people. On August 14, 2026, Google began a gradual rollout, up to 15 days for feature visibility, of new admin controls for calendar invitations that apply to new and existing users. Admins can now decide which of the three options staff are allowed to pick, at the organizational unit or group level, and Google said the point is inbound events from unknown senders and the content inside them.

The new control is set to From everyone by default. That is the same open door the phishing volume has been walking through. Some campuses have already locked it. Binghamton University told staff in September 2026 that calendars would sit on Only if the sender is known, and that users could not choose a weaker setting. Unknown senders still get an email; the event just does not appear on the grid until someone confirms the sender. Google also says the change covers future invitations only, so old spam events have to be cleared by hand.

Microsoft 365 has its own version of the same design, which is why Sublime’s samples show Google first and Microsoft next. Calendar files remain a small share of all bad payloads on Microsoft’s own tally, about 4% in Q2, and they are growing because they skip the click that every awareness poster still talks about.

Passkeys Close the Login Hole

Mathew Woodyard, director of threat intelligence at identity firm Okta, does not think a sharper eye for a fake invite is the fix, because the invites increasingly look identical to real ones. He wants a sign-in that cannot be typed into a mock-up page.

The strongest mitigation isn’t user education about ‘spotting a fake invite,’ since the invites increasingly look identical to legitimate ones. It’s giving users something that can’t be phished in the first place.

Mathew Woodyard, director of threat intelligence, Okta

That something is a passkey. The FIDO Alliance, which maintains the standards behind them, says passkeys are phishing-resistant by design: a device-held cryptographic key, unlocked with a biometric, PIN, or pattern, and bound to the real site so a look-alike domain gets a signature the real server rejects. Woodyard’s warning is that this only works as a default, not as an opt-in sitting next to a password that a fake Drive page can still harvest.

Passkeys also do not cover the rest of the calendar job. They do not stop a callback number in a voicemail lure, a ScreenConnect installer on a credit-note page, or a deepfake on a video call that never asks for a login. They close the fake Google or Microsoft sign-in. The event can still sit on the grid, ping a reminder, and wait for a tired click.

Until Workspace tenants move off From everyone, that grid remains a second inbox most filters never see. The meeting you do not remember booking may be the one that did not need you to book it.