Google released the first part of its June 2021 spam update on 23rd Jun, announcing: "As part of our regular work to improve results, we've released a spam update to our systems."
The same announcement set the schedule: "This spam update will conclude today. A second one will follow next week."
Search Engine Land's coverage noted Google pointed sites to its best practices for Search rather than naming specific spam types.
Part two arrived on 28th Jun 2021. Google said "The second part of our spam update has begun today, and it will also conclude later today, unless we share otherwise".
Coverage of the second part reported it as a global rollout. It affected both web and image results.
Same-day spam deployments like these contrasted with core updates. At the time, core updates typically ran one to two weeks.
Spam updates are periodic improvements to Google's automated spam-detection systems, so sites playing by the rules should see no change.
If your rankings dropped around 23rd Jun or 28th Jun 2021, audit the site against Google's spam policies. Fix what violates them.
Per Google's spam updates documentation, improvement then depends on its systems learning "over a period of months" that the site complies.
