diff --git a/squinnondation/hazel.py b/squinnondation/hazel.py
index 27dea5f..a8c07f4 100644
--- a/squinnondation/hazel.py
+++ b/squinnondation/hazel.py
@@ -15,7 +15,7 @@ class Hazelnut:
     """
     A hazelnut is a connected client, with its socket.
     """
-    def __init__(self, nickname: str = "anonymous", address: str = "localhost", port: int = 2500):
+    def __init__(self, nickname: str = None, address: str = "localhost", port: int = 2500):
         self.nickname = nickname
 
         try:
@@ -174,7 +174,7 @@ class Squirrel(Hazelnut):
         elif key != "\n":
             # Insert the pressed key in the current message
             new_buffer = self.input_buffer[:self.input_index] + key + self.input_buffer[self.input_index:]
-            if len(DataTLV.construct(f"<{self.nickname}> {new_buffer}")) > 255 - 8 - 4:
+            if len(DataTLV.construct(f"{self.nickname}: {new_buffer}")) > 255 - 8 - 4:
                 # The message is too long to be sent once. We don't allow the user to type any other character.
                 curses.beep()
                 return
@@ -190,7 +190,7 @@ class Squirrel(Hazelnut):
         if not msg:
             return
 
-        msg = f"<{self.nickname}> {msg}"
+        msg = f"{self.nickname}: {msg}"
         self.add_message(msg)
 
         pkt = Packet.construct(DataTLV.construct(msg))
@@ -257,7 +257,7 @@ class Squirrel(Hazelnut):
         Add a new system log message.
         TODO: Configure logging levels to ignore some messages.
         """
-        return self.add_message(f"<system> *{msg}*")
+        return self.add_message(f"system: *{msg}*")
 
     def print_markdown(self, pad: Any, y: int, x: int, msg: str,
                        bold: bool = False, italic: bool = False, underline: bool = False, strike: bool = False) -> int:
@@ -363,6 +363,8 @@ class Squirrel(Hazelnut):
             if i + y_offset > curses.LINES - 3:
                 break
 
+            msg = re.sub("([^:]*): (.*)", "<\\1> \\2", msg, 1)
+
             if not re.match("<.*> .*", msg):
                 msg = "<unknown> " + msg
             match = re.match("<(.*)> (.*)", msg)
diff --git a/squinnondation/messages.py b/squinnondation/messages.py
index 869ae87..fd9d672 100644
--- a/squinnondation/messages.py
+++ b/squinnondation/messages.py
@@ -1,6 +1,6 @@
 # Copyright (C) 2020 by eichhornchen, ÿnérant
 # SPDX-License-Identifier: GPL-3.0-or-later
-
+import re
 from typing import Any, List, Optional
 from ipaddress import IPv6Address
 from enum import Enum
@@ -207,7 +207,21 @@ class DataTLV(TLV):
         A message has been sent. We log it.
         TODO: Check that the tuple (sender_id, nonce) is unique to avoid duplicates.
         """
-        squirrel.add_message(self.data.decode('UTF-8'))
+        msg = self.data.decode('UTF-8')
+        squirrel.add_message(msg)
+        nickname_match = re.match("(.*): (.*)", msg)
+        if nickname_match is None:
+            squirrel.send_packet(sender, Packet.construct(WarningTLV.construct(
+                "Unable to retrieve your username. Please use the syntax 'nickname: message'")))
+        else:
+            nickname = nickname_match.group(1)
+            if sender.nickname is None:
+                sender.nickname = nickname
+            elif sender.nickname != nickname:
+                squirrel.send_packet(sender, Packet.construct(WarningTLV.construct(
+                    "It seems that you used two different nicknames. "
+                    f"Known nickname: {sender.nickname}, found: {nickname}")))
+                sender.nickname = nickname
 
     @staticmethod
     def construct(message: str) -> "DataTLV":
@@ -281,7 +295,7 @@ class WarningTLV(TLV):
     def unmarshal(self, raw_data: bytes) -> None:
         self.type = raw_data[0]
         self.length = raw_data[1]
-        self.message = raw_data[2:self.length].decode("UTF-8")
+        self.message = raw_data[2:self.length + 2].decode("UTF-8")
 
     def marshal(self) -> bytes:
         return self.type.to_bytes(1, sys.byteorder) + \
@@ -289,7 +303,15 @@ class WarningTLV(TLV):
             self.message.encode("UTF-8")[:self.length]
 
     def handle(self, squirrel: Any, sender: Any) -> None:
-        squirrel.add_message(f"<warning> *A client warned you: {self.message}*")
+        squirrel.add_message(f"warning: *A client warned you: {self.message}*")
+
+    @staticmethod
+    def construct(message: str) -> "WarningTLV":
+        tlv = WarningTLV()
+        tlv.type = 7
+        tlv.message = message
+        tlv.length = len(tlv.message.encode("UTF-8"))
+        return tlv
 
 
 class Packet: