You can now send alerts to Private Slack channels in addition to public channels.
When creating or editing an alert, under Notifications -> Alert Channel, the Slack Channel(s) dropdown will display first the list of public channels and then the list of private channels. You can search and select from the channels available.
Only channels that have the ChurnZero Slack ChatBot invited to it will show. To remove a channel from the list, simple remove the ChatBot from that channel.
To find out more about Alerts to Slack channels, read here.