If you've ever had an account or relationship with Slack, it's worth checking whether your personal data was exposed in this incident. Here's what happened, what data was involved, and what to do about it.
What Happened
Slack disclosed in March 2015 that unauthorized access had occurred to its central user database over a four-day period in February 2015. The attackers gained access to infrastructure that stored user profile information.
What Data Was Exposed
The exposed data included usernames, email addresses, hashed passwords, and phone numbers or Skype IDs where users had chosen to provide them. Slack stated no plaintext passwords or message content was accessed.
Why This Still Matters
Exposed data doesn't expire. It's sold, traded, and reused for years, fueling credential stuffing attacks — automated attempts to reuse your email and password combination across other sites. If you reused a password anywhere, one old exposure can compromise several current accounts.
How to Check If You Were Affected
Use our free breach checker below — enter your email and we'll scan it against known breach databases instantly, no signup required.
What to Do If You Were Affected
- Change any reused password immediately, starting with your most sensitive accounts.
- Enable two-factor authentication wherever it's offered.
- Monitor financial and health accounts closely if that kind of data was involved.
- Watch for phishing — exposed data is often used to craft convincing scam messages.
- Freeze your credit if your SSN or government ID number was exposed.
👉 Check your own exposure in 30 seconds → scan your email free.
Frequently Asked Questions
When did the Slack data breach happen?
Slack detected unauthorized access to its central user database that occurred over approximately four days in February 2015, and disclosed the incident publicly on 27 March 2015.
What data was stolen in the Slack breach?
Usernames, email addresses, hashed passwords, and optionally provided phone numbers or Skype IDs were exposed. Slack confirmed message content and files were not accessed in this incident.
How do I check if my Slack account was affected?
Use the free checker at Scan My Shadow with your email address. If your account predates February 2015 and you never changed your password since, change it now.
Did Slack add extra security after the breach?
Yes, Slack introduced two-factor authentication for all users shortly after this incident as a direct response to the breach.
Was this the only Slack security incident?
Slack also disclosed a separate, more limited 2022 incident involving stolen employee credentials that exposed a portion of Slack's own source code repositories, but that incident did not involve customer message data or account credentials.