The following occurred - while updating the configuration of our internal caching system, Varnish, for a few minutes the system began to issue cached pages from the users who most recently visited the same page, as the system considered this the most relevant source of data. Thus, for 3 minutes, some users may have seen pages which appeared as though they were logged in as another random account, but it was actually just a snapshot of the page of the last visitor. It had no effect on security, as it was not possible to perform any actions on behalf of this other account. When attempting to load another page during these few minutes, another cached page was served in most cases.
This issue primarily affected people in the United States; the Russian-speaking audience was almost completely unaffected because the changes occurred very late at night in Russia. However, we are grateful to those of you who noticed this and quickly brought our attention to the issue, which gave us the opportunity to quickly understand the cause and resolve it.
The changes which were made are intended to improve site security, and reduce malicious activity on the site. It will make it more difficult to steal cookies from public locations, or spoof them for malicious attacks. We're also working on a few other things:
- Better communication with our 3rd party developers
- More thorough testing before rolling out changes
- Finally, better communication with you about our development process
Again, please accept our apologies for any inconvenience.