In the process of turning our subscription systems over to API based subscribers, we created a new yahoo subscriber using OAuth and the Yahoo APIs. This is a replacement for the old crawler-based subscription source. A new update task "com.openexchange.subscribe.yahoo.update.DeleteOldYahooSubscriptions" has been introduced to remove all crawler based yahoo subscriptions. Since this is too radical a step for a public Patch Release, the new subscriber "open-xchange-subscribe-yahoo" is an optional package, and the update task is excluded via the "excludedupdatetasks.properties" configuration file.
If you don't use subscriptions anyway, don't do anything.
If you provide yahoo as a valid subscription source, but would like to keep the old subscriptions, with all the limitations of the crawler based subscriptions (i.e. vulnerability to changes on the web pages and being generally error prone), don't do anything.
If you want to provide a reliable, API based Yahoo subscription source (or are reasonably sure, that no yahoo subscriptions exist anyway, since, for example, they were disabled up until now), install "open-xchange-subscribe-yahoo" and comment out the line "com.openexchange.subscribe.yahoo.update.DeleteOldYahooSubscriptions" in the "excludedupdatetasks.properties" file. Note though that this removes all existing yahoo subscriptions, so your users will have to recreate them, using the new 6.20 OAuth mechanisms.