diff --git a/dist/socket.js b/dist/socket.js
index 3ce0ab7201..a4ef75cac7 100644
--- a/dist/socket.js
+++ b/dist/socket.js
@@ -9,6 +9,7 @@ const socket_io_parser_1 = require("socket.io-parser");
 const has_binary2_1 = __importDefault(require("has-binary2"));
 const url_1 = __importDefault(require("url"));
 const debug_1 = __importDefault(require("debug"));
+const base64id_1 = __importDefault(require("base64id"));
 const debug = debug_1.default("socket.io:socket");
 /**
  * Blacklisted events.
@@ -40,7 +41,7 @@ class Socket extends events_1.EventEmitter {
         this._rooms = new Set();
         this.server = nsp.server;
         this.adapter = this.nsp.adapter;
-        this.id = nsp.name !== "/" ? nsp.name + "#" + client.id : client.id;
+        this.id = base64id_1.default.generateId(); // don't reuse the Engine.IO id because it's sensitive information
         this.connected = true;
         this.disconnected = false;
         this.handshake = this.buildHandshake(auth);
@@ -206,7 +207,7 @@ class Socket extends events_1.EventEmitter {
         debug("socket connected - writing packet");
         this.nsp.connected.set(this.id, this);
         this.join(this.id);
-        this.packet({ type: socket_io_parser_1.PacketType.CONNECT });
+        this.packet({ type: socket_io_parser_1.PacketType.CONNECT, data: { sid: this.id } });
     }
     /**
      * Called with each packet. Called by `Client`.
diff --git a/lib/socket.ts b/lib/socket.ts
index 3735deebcf..fcfc456bb7 100644
--- a/lib/socket.ts
+++ b/lib/socket.ts
@@ -6,6 +6,7 @@ import debugModule from "debug";
 import { Client, Namespace, Server } from "./index";
 import { IncomingMessage } from "http";
 import { Adapter, BroadcastFlags, Room, SocketId } from "socket.io-adapter";
+import base64id from "base64id";
 
 const debug = debugModule("socket.io:socket");
 
@@ -100,7 +101,7 @@ export class Socket extends EventEmitter {
     super();
     this.server = nsp.server;
     this.adapter = this.nsp.adapter;
-    this.id = nsp.name !== "/" ? nsp.name + "#" + client.id : client.id;
+    this.id = base64id.generateId(); // don't reuse the Engine.IO id because it's sensitive information
     this.connected = true;
     this.disconnected = false;
     this.handshake = this.buildHandshake(auth);
@@ -288,7 +289,7 @@ export class Socket extends EventEmitter {
     debug("socket connected - writing packet");
     this.nsp.connected.set(this.id, this);
     this.join(this.id);
-    this.packet({ type: PacketType.CONNECT });
+    this.packet({ type: PacketType.CONNECT, data: { sid: this.id } });
   }
 
   /**
diff --git a/package.json b/package.json
index cb86b9b2ae..6b14335bfa 100644
--- a/package.json
+++ b/package.json
@@ -27,6 +27,7 @@
     "format:fix": "prettier --write 'lib/**/*.ts' 'test/**/*.ts'"
   },
   "dependencies": {
+    "base64id": "~2.0.0",
     "debug": "~4.1.0",
     "engine.io": "~4.0.0",
     "has-binary2": "~1.0.2",