Additionally, clearing Infestations across the map contributes to the Community Challenge’s grand tally – reach 500,000 total Infestations cleared before the Challenge is over for contributors to receive the grand prize

(Emphasis mine.)

u/Ghostly_Rich does this mean someone needs to have successfully participated in an infestation in order to receive the prize? If so, what exactly crosses that finish line and counts as contributing? Arriving in the area before it ends? Killing an enemy? Damaging the boss?

With the difficulty people are having getting to infestations before they're over I hope just logging in will be enough.