ChatGPT’s chat history feature is has been offline for several days, after a bug exposed brief descriptions of other users’ conversations to people on the service on Monday.

On Reddit, one user posted a photo showing descriptions of several ChatGPT conversations they said weren’t their own, while someone else on Twitter posted a screenshot of the same bug. A spokesperson for OpenAI confirmed the incident to Bloomberg, noting that the bug did not share full transcripts of conversations but only brief descriptive titles.

The issue was caused by “a bug in an open source library,” according to a tweet from OpenAI CEO Sam Altman, who says that a technical postmortem will be coming later. He also says that a fix for the library has been released and that OpenAI has validated it, but didn’t mention when users could expect to see their chat histories again.

The bug is an important reminder to be careful about the sensitive information shared with ChatGPT. “Please don’t share any sensitive information in your conversations,” warns an FAQ on OpenAI’s website, which notes that the company cannot delete specific prompts from a person’s history, and that conversations may be used for training. However, there will inevitably be a strong temptation to share confidential information with the chatbot, particularly as businesses continue to experiment with how to make use of the new tool. 

Bloomberg reports that OpenAI temporarily shut down ChatGPT on Monday in response to the bug, but that it was brought back online later that night. As of this writing the chat history sidebar has been replaced with a message noting that “History is temporarily unavailable” and that the company is “working to restore this feature as soon as possible.”

The last update on OpenAI’s status page from 10:54PM ET on Monday notes that service has been restored, but it’s still working to bring back past conversation histories for all users. However, according to Altman, users won’t have access to chats they did from 4AM ET to 1PM ET on March 27th.

Update March 22nd, 4:45PM ET: Added confirmation from Sam Altman that the chat history issue was due to a bug in a piece of open-source software and that users wouldn’t be able to access their chat history from a few hours on Monday.