Slack

Is Slack safe?

Yes, for the job it is built for. Slack keeps work conversations off personal phones and email, has never been fined by a privacy regulator as far as we could find, and does not track you across other apps. We score it 65/100, a little above Microsoft Teams (63) and below Zoom (71).

The weak point is not Slack's servers but the access tokens on employees' computers. When an attacker steals one, they can read years of a company's conversations. And because nothing is end-to-end encryptedEnd-to-end encryptionEncryption in which only the sender and the recipient can read a message. The company running the service cannot see its content.More in the glossary, everything you type is readable by Slack and, in most cases, by your employer.

How workspaces get breached

Slack's own code was stolen this way. In its notice, Slack said that on 27 December 2022 an attacker used "a limited number of Slack employee tokens" to download private code repositories from its GitHub account. Slack said customer data was not in the repositories.

Customers have been hit the same way:

• Disney, 2024. A group called Nullbulge published more than a terabyte of data from Disney's internal Slack channels. Computerworld, citing the Wall Street Journal, reported that Disney planned to move to Microsoft Teams.
• Nikkei, 2025. The Japanese publisher said malware on an employee's personal computer stole Slack login credentials, potentially exposing names, email addresses and chat histories of 17,368 people.

In both cases the company was breached through a person, not a flaw in Slack. That is the real lesson: a Slack workspace is only as safe as the least protected laptop logged into it.

Who can read your messages

Slack encrypts data in transit and at rest. Enterprise customers can hold their own encryption keys with Enterprise Key Management, which lets them cut off access to their data. There is no end-to-end encryptionEnd-to-end encryptionEncryption in which only the sender and the recipient can read a message. The company running the service cannot see its content.More in the glossary for messages, huddles or files.

Your employer has wide powers. According to Slack's export documentation, owners and admins on any plan can export public channels. On Business+, owners can apply for exports that include private channels and direct messages, and Enterprise plans support full compliance exports. Retention is set by the workspace. On the Free plan, messages and files are kept for only one year.

Data and AI training

Apple's privacy label for Slack lists no "Data Used to Track You". Name, email address, coarse location and user and device IDs are used for Slack's own advertising and marketing, and browsing history, contacts and content feed analytics.

The AI question flared in May 2024, when users noticed that Slack's privacy principles allowed customer data to train its models. Slack's current principles say it does not use customer data to train generative AI models without opt-in consent. It does, by default, use it to train global machine-learning models behind features such as channel and emoji suggestions. Opting out is not a switch: a workspace owner has to email Slack and wait for confirmation. Individual users cannot opt out themselves.

Slack outside work

Many open-source projects, hobby groups and online courses run free Slack communities. These are less controlled than a company workspace: anyone with the invite link can join, see the member list and send direct messages. Community admins can export public channels, and the one-year history limit means old conversations vanish. For a large public community with strangers, Discord has more moderation tools; for private chats with friends, an end-to-end encryptedEnd-to-end encryptionEncryption in which only the sender and the recipient can read a message. The company running the service cannot see its content.More in the glossary messenger is a better fit.

How to use Slack safely

1. Turn on two-factor authenticationTwo-factor authenticationSigning in with a second proof of identity on top of your password, such as a code from an app, a security key or a passkey.More in the glossary, or make sure your company enforces single sign-on with it.
2. Do not log into a work Slack from a personal computer you share or do not keep updated. Token-stealing malware is the main way workspaces are breached.
3. Treat Slack Connect invitations and DMs from outside organisations like email from strangers.
4. Keep passwords, API keys and customer data out of channels. Attackers who get in search for them first.
5. If you are an owner and want to keep your data out of Slack's global models, email Slack to opt out.

How we scored it

The regulatory record (85) is Slack's strongest factor, with no significant fine or order found. Transparency and control (58) is the weakest: the employer decides retention and export, and the AI opt-out depends on an email from the owner. Privacy and security (62 each) reflect a restrained App Store label but no end-to-end encryptionEnd-to-end encryptionEncryption in which only the sender and the recipient can read a message. The company running the service cannot see its content.More in the glossary and repeated workspace breaches through stolen tokens.