diff --git a/server/src/scripts/create-private-threads.js b/server/src/scripts/create-private-threads.js
new file mode 100644
index 000000000..a07bc844b
--- /dev/null
+++ b/server/src/scripts/create-private-threads.js
@@ -0,0 +1,71 @@
+// @flow
+
+import bots from 'lib/facts/bots.json';
+import { threadTypes } from 'lib/types/thread-types';
+
+import { getRolePermissionBlobsForChat } from '../creators/role-creator';
+import { dbQuery, SQL } from '../database/database';
+import { createScriptViewer } from '../session/scripts';
+import {
+  commitMembershipChangeset,
+  recalculateAllPermissions,
+} from '../updaters/thread-permission-updaters';
+import { main } from './utils';
+
+async function markThreadsAsPrivate() {
+  const findThreadsToUpdate = SQL`
+    SELECT t.id, r.id AS role
+    FROM (
+      SELECT t.id
+      FROM threads t
+      INNER JOIN memberships m
+        ON m.thread = t.id
+      WHERE t.type = ${threadTypes.CHAT_SECRET}
+      GROUP BY id
+      HAVING
+        COUNT(m.thread) = 1
+    ) t
+    INNER JOIN roles r ON r.thread = t.id
+  `;
+  const [result] = await dbQuery(findThreadsToUpdate);
+  const threadIDs = result.map((row) => row.id);
+
+  if (threadIDs.length === 0) {
+    return;
+  }
+
+  const description =
+    'This is your private thread, ' +
+    'where you can set reminders and jot notes in private!';
+
+  const updateThreads = SQL`
+    UPDATE threads
+    SET type = ${threadTypes.PRIVATE}, description = ${description}
+    WHERE id IN (${threadIDs})
+  `;
+
+  const defaultRolePermissions = getRolePermissionBlobsForChat(
+    threadTypes.PRIVATE,
+  ).Members;
+  const defaultRolePermissionString = JSON.stringify(defaultRolePermissions);
+  const viewer = createScriptViewer(bots.squadbot.userID);
+  const permissionPromises = result.map(async ({ id, role }) => {
+    console.log(`Updating thread ${id} and role ${role}`);
+    const updatePermissions = SQL`
+      UPDATE roles
+      SET permissions = ${defaultRolePermissionString}
+      WHERE id = ${role}
+    `;
+    await dbQuery(updatePermissions);
+
+    const changeset = await recalculateAllPermissions(
+      id.toString(),
+      threadTypes.PRIVATE,
+    );
+    return await commitMembershipChangeset(viewer, changeset);
+  });
+
+  await Promise.all([dbQuery(updateThreads), ...permissionPromises]);
+}
+
+main([markThreadsAsPrivate]);