diff --git a/CHANGELOG.md b/CHANGELOG.md
index b84478f..f705852 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,11 @@ The format is based on [Semantic Versioning](https://semver.org/).
 ### Added
 - GitHub Actions workflow (`.github/workflows/deploy.yml`): pull requests into `main` are checked (all Python files must compile), and merging into `main` updates and restarts the bot on the server over SSH through `tools/deploy.sh`, using a key that can only run that script. Setup: `docs/deploy.md`.
 
+### Fixed
+- Anyone logged in with a shared account (e.g. `murid`) could delete that account for everyone with `/du murid` + `y`, because the bot treated it as deleting their own account. Accounts listed in the new `SHARED_ACCOUNTS` setting (default `tamu`, `murid`, `hadirin`, `osis`, `guest`) cannot be deleted via the bot, not even by admins.
+- Join/login spam detection counted everyone on a shared account behind one IP (all students on `murid` from the school network) as one person. For shared accounts it now tells people apart by nickname + IP.
+- Channels created by a shared account (owned by e.g. `murid`) could be deleted or given away by anyone on that account. Non-admin shared accounts can no longer create, delete or transfer channels via the bot; admin accounts (`pemateri`, `F.OSIS`) keep their admin rights. `pemateri` and `f.osis` are in the default `SHARED_ACCOUNTS`.
+
 ### Changed
 - The shipped badword list is now `badwords/default_words.txt`; `badwords/words.txt` (with the admins' `/bwa`/`/bwd` edits) is git-ignored and created from the default list on first run, so updates no longer conflict with or overwrite those edits.
 - `TeamTalkBot.service` is a template for a non-root account and logs to the journal.
diff --git a/README.md b/README.md
index 97c108a..be91f25 100644
--- a/README.md
+++ b/README.md
@@ -65,6 +65,7 @@ All settings live in `config.json`. Highlights:
 | **Lifecycle** | `CHANNEL_INACTIVITY_TIMEOUT` (`{"value": X, "unit": "days"}`), `CHANNEL_DELETION_WARNING_SECONDS` |
 | **Channel Rules** | `CHANNEL_CREATION_MAX_PER_USER`, limit/block messages, `CHANNEL_CREATION_BLOCKED_USERNAMES` |
 | **Registration** | `REGISTRATION_ALLOWED_USERNAMES`, per-IP limits/messages |
+| **Shared accounts** | `SHARED_ACCOUNTS` – accounts many people log in with (default `tamu`, `murid`, `hadirin`, `osis`, `pemateri`, `f.osis`, `guest`): not deletable via the bot, moderation tells their users apart by nickname + IP, and unless they are admin accounts they cannot create, delete or transfer channels via the bot |
 | **Abuse Throttling** | `ABUSE_LOGIN_ENABLED`, `ABUSE_JOIN_ENABLED`, `ABUSE_LOGIN_COUNT`, `ABUSE_JOIN_COUNT`, `BADWORD_ABUSE_COUNT`, `ABUSE_WINDOW_SEC`, `ABUSE_TEMP_BAN_MINUTES`, `BAN_TARGET`, `ABUSE_WHITELIST_FILE`, warning message arrays |
 | **Message Anti-Spam** | `ANTISPAM_MESSAGE_ENABLED`, `ANTISPAM_MESSAGE_COUNT`, `ANTISPAM_MESSAGE_WINDOW_SEC`, `ANTISPAM_INTERCEPT_TYPES`, `ANTISPAM_IGNORE_ADMINS`, warning message arrays |
 | **Badwords** | `BADWORDS_ENABLED`, `BADWORDS_INTERCEPT_TYPES` (`"PRIVATE"`, `"CHANNEL"`, `"BROADCAST"`), `BADWORDS_FILE`, `BADWORDS_IGNORE_ADMINS`, `BADWORDS_PROFILE_CHECK_ENABLED` |
diff --git a/config.py b/config.py
index 74d2743..2168cf9 100644
--- a/config.py
+++ b/config.py
@@ -89,6 +89,12 @@
 CHANNEL_CREATION_BLOCKED_MESSAGE: str = "You are not permitted to create channels."
 REGISTRATION_ALLOWED_USERNAMES: List[str] = ["guest"]
 REGISTRATION_NOT_ALLOWED_MESSAGE: str = "You already have a registered account and do not need to register again."
+# Accounts that many people log in with. They cannot be deleted via the bot,
+# moderation tells their users apart by nickname + IP instead of username, and
+# (unless they are admin accounts) they cannot create or manage channels.
+SHARED_ACCOUNTS: List[str] = [
+    "tamu", "murid", "hadirin", "osis", "pemateri", "f.osis", "guest",
+]
 REGISTRATION_IP_LIMIT: int = 1
 REGISTRATION_IP_WINDOW_MINUTES: int = 2880
 REGISTRATION_IP_LIMIT_MESSAGE: str = "Account creation failed: your IP has reached the registration limit. Please try again later."
@@ -173,6 +179,7 @@
     "CHANNEL_CREATION_BLOCKED_MESSAGE": CHANNEL_CREATION_BLOCKED_MESSAGE,
     "REGISTRATION_ALLOWED_USERNAMES": REGISTRATION_ALLOWED_USERNAMES,
     "REGISTRATION_NOT_ALLOWED_MESSAGE": REGISTRATION_NOT_ALLOWED_MESSAGE,
+    "SHARED_ACCOUNTS": SHARED_ACCOUNTS,
     "REGISTRATION_IP_LIMIT": REGISTRATION_IP_LIMIT,
     "REGISTRATION_IP_WINDOW_MINUTES": REGISTRATION_IP_WINDOW_MINUTES,
     "REGISTRATION_IP_LIMIT_MESSAGE": REGISTRATION_IP_LIMIT_MESSAGE,
diff --git a/docs/index.html b/docs/index.html
index f992a81..cfa517c 100644
--- a/docs/index.html
+++ b/docs/index.html
@@ -81,6 +81,7 @@ <h3>Channel Creation Rules</h3>
   </ul>
   <h3>Registration Policy</h3>
   <ul>
+    <li><code>SHARED_ACCOUNTS</code>: accounts that many people log in with (default <code>tamu</code>, <code>murid</code>, <code>hadirin</code>, <code>osis</code>, <code>pemateri</code>, <code>f.osis</code>, <code>guest</code>). They cannot be deleted via the bot (<code>/du</code>), even by admins, and join/login spam detection tells their users apart by nickname + IP instead of username. Non-admin shared accounts cannot create, delete or transfer channels via the bot (a channel owned by <code>murid</code> would belong to every student); admin accounts keep their admin rights.</li>
     <li><code>REGISTRATION_ALLOWED_USERNAMES</code>: usernames (case-insensitive) that may request new accounts. Typically <code>["guest"]</code> to limit spammers.</li>
     <li><code>REGISTRATION_NOT_ALLOWED_MESSAGE</code>: text sent when disallowed users attempt registration.</li>
     <li><code>REGISTRATION_IP_LIMIT</code>, <code>REGISTRATION_IP_WINDOW_MINUTES</code>, <code>REGISTRATION_IP_LIMIT_MESSAGE</code>: per-IP quota, window length, and message when quota is exceeded.</li>
diff --git a/help_texts.py b/help_texts.py
index b969eb6..5e89398 100644
--- a/help_texts.py
+++ b/help_texts.py
@@ -67,7 +67,8 @@
     ),
     "rc": (
         "Create Channel",
-        "Create a new channel under the configured parent path.\n"
+        "Create a new channel under the configured parent path. Not available on shared "
+        "accounts such as murid or tamu (ask an admin).\n"
         "Format:\n"
         "  /rc <channel_name>\n\n"
         "Interactive flow:\n"
@@ -107,7 +108,8 @@
         "- Without --force the bot asks for 'y' or 'n'.\n\n"
         "Permissions:\n"
         "- Admins: may delete any username.\n"
-        "- Non-admins: may only delete their own account.\n\n"
+        "- Non-admins: may only delete their own account.\n"
+        "- Shared accounts (e.g. murid, tamu, hadirin, osis) cannot be deleted via the bot.\n\n"
         "Examples:\n"
         "  /du alex\n"
         "  /du alex --force\n",
diff --git a/tt_client.py b/tt_client.py
index 134eb27..f532581 100644
--- a/tt_client.py
+++ b/tt_client.py
@@ -1993,6 +1993,10 @@ def _can_user_create_channel(self, requester_id: int) -> bool:
         if blocklist and uname_lower in blocklist:
             self.send_pm(requester_id, self._channel_creation_blocked_message())
             return False
+        if self._is_shared_account(uname_lower) and not self._is_admin(requester_id):
+            # Owned by "murid", a channel would belong to every student
+            self.send_pm(requester_id, self._SHARED_NO_CHANNELS)
+            return False
         max_channels = self._channel_creation_max_per_user()
         if max_channels > 0:
             owned = self._channel_creation_owned_count(username)
@@ -2408,11 +2412,27 @@ def _in_login_sync(self) -> bool:
         """True while the server replays already-online users after our login."""
         return self._now() < self._login_sync_until
 
+    def _is_shared_account(self, username: str) -> bool:
+        values = getattr(config, "SHARED_ACCOUNTS", []) or []
+        return str(username or "").strip().lower() in {str(v).strip().lower() for v in values}
+
     def _person_key(self, user: User) -> Optional[Tuple[str, str]]:
-        """Identify a person across sessions by (username, IP)."""
+        """Identify a person across sessions by (username, IP).
+
+        On a shared account (SHARED_ACCOUNTS, e.g. all students on "murid")
+        the username says nothing about who it is, so the nickname is used
+        as well; otherwise everyone on that account behind one IP would count
+        as one person.
+        """
         username = from_tt_char(user.szUsername).strip().lower()
         ip = from_tt_char(user.szIPAddress).strip()
-        return (username, ip) if username and ip else None
+        if not username or not ip:
+            return None
+        if self._is_shared_account(username):
+            nickname = from_tt_char(user.szNickname).strip().lower()
+            if nickname:
+                return (f"{username}/{nickname}", ip)
+        return (username, ip)
 
     def _is_reconnect(self, user: User) -> bool:
         """Whether this login looks like a reconnect after a dropped connection.
@@ -2792,11 +2812,19 @@ def _handle_delete_channel(self, requester_id: int, target: str, force: bool):
             return
         self._perform_delete_channel(requester_id, path)
 
+    _SHARED_NO_CHANNELS = (
+        "Shared accounts cannot create or manage channels via the bot, because everyone "
+        "on the account would own them. Ask an admin."
+    )
+
     def _check_delete_channel_allowed(self, requester_id: int, path: str) -> bool:
         # Authorization: admins can delete any channel; non-admins only their own (based on cache)
         if self._is_admin(requester_id):
             return True
         requester_username = self._get_username(requester_id)
+        if self._is_shared_account(requester_username):
+            self.send_pm(requester_id, self._SHARED_NO_CHANNELS)
+            return False
         owner = cache_store.get_owner(path)
         if owner and owner == requester_username:
             return True
@@ -2869,6 +2897,19 @@ def _handle_delete_user(self, requester_id: int, username: str, force: bool):
                 "Delete user denied; empty username (requester=%s)", requester_id
             )
             return
+        if self._is_shared_account(username):
+            # Deleting it would lock out everyone who logs in with it
+            self.send_pm(
+                requester_id,
+                f"'{username}' is a shared account (SHARED_ACCOUNTS) and cannot be deleted "
+                "via the bot. An admin can still remove it in the TeamTalk client.",
+            )
+            logger.warning(
+                "Delete of shared account refused (requester=%s, target=%s)",
+                requester_id,
+                username,
+            )
+            return
         allowed_usernames = self._registration_allowed_usernames()
         if allowed_usernames and username.lower() in allowed_usernames:
             self.send_pm(requester_id, "This account cannot be deleted via the bot.")
@@ -3049,6 +3090,9 @@ def _handle_transfer_owner(self, requester_id: int, target: str, username: str):
         # Reuse admin check helper for clarity
         is_admin = self._is_admin(requester_id)
         requester_username = self._get_username(requester_id)
+        if not is_admin and self._is_shared_account(requester_username):
+            self.send_pm(requester_id, self._SHARED_NO_CHANNELS)
+            return
         if not is_admin:
             if not current or current != requester_username:
                 self.send_pm(