diff --git a/anonstream/__init__.py b/anonstream/__init__.py
index cc6af77..a66403e 100644
--- a/anonstream/__init__.py
+++ b/anonstream/__init__.py
@@ -42,6 +42,8 @@ def create_app(config_file):
         'CHAT_NAME_MAX_LENGTH': config['chat']['max_name_length'],
         'CHAT_NAME_MIN_CONTRAST': config['chat']['min_name_contrast'],
         'CHAT_BACKGROUND_COLOUR': color_to_colour(config['chat']['background_color']),
+        'FLOOD_DURATION': config['flood']['duration'],
+        'FLOOD_THRESHOLD': config['flood']['threshold'],
         'CAPTCHA_LIFETIME': config['captcha']['lifetime'],
         'CAPTCHA_FONTS': config['captcha']['fonts'],
         'CAPTCHA_ALPHABET': config['captcha']['alphabet'],
diff --git a/anonstream/captcha.py b/anonstream/captcha.py
index a4b9f5e..34e8e9c 100644
--- a/anonstream/captcha.py
+++ b/anonstream/captcha.py
@@ -35,6 +35,12 @@ def get_random_captcha_digest():
 
     return digest
 
+def get_random_captcha_digest_for(user):
+    if user['verified']:
+        return None
+    else:
+        return get_random_captcha_digest()
+
 def get_captcha_image(digest):
     try:
         captcha = CAPTCHAS[digest]
diff --git a/anonstream/routes/nojs.py b/anonstream/routes/nojs.py
index 6d21617..707a5c9 100644
--- a/anonstream/routes/nojs.py
+++ b/anonstream/routes/nojs.py
@@ -1,9 +1,9 @@
 from quart import current_app, request, render_template, redirect, url_for, escape, Markup
 
-from anonstream.captcha import get_random_captcha_digest
+from anonstream.captcha import get_random_captcha_digest_for
 from anonstream.chat import add_chat_message, Rejected
 from anonstream.stream import get_stream_title
-from anonstream.user import add_state, pop_state, try_change_appearance, verify, BadCaptcha
+from anonstream.user import add_state, pop_state, try_change_appearance, verify, deverify, BadCaptcha
 from anonstream.routes.wrappers import with_user_from, render_template_with_etag
 from anonstream.helpers.chat import get_scrollback
 from anonstream.helpers.user import get_default_name
@@ -45,14 +45,13 @@ async def nojs_form(user):
     state_id = request.args.get('state', type=int)
     state = pop_state(user, state_id)
     prefer_chat_form = request.args.get('landing') != 'appearance'
-    digest = None if user['verified'] else get_random_captcha_digest()
     return await render_template(
         'nojs_form.html',
         user=user,
         state=state,
         prefer_chat_form=prefer_chat_form,
         nonce=generate_nonce(),
-        digest=digest,
+        digest=get_random_captcha_digest_for(user),
         default_name=get_default_name(user),
     )
 
@@ -86,7 +85,7 @@ async def nojs_submit_message(user):
     else:
         nonce = form.get('nonce', '')
         try:
-            # if the comment is empty but the captcha was just solved,
+            # If the comment is empty but the captcha was just solved,
             # be lenient: don't raise an exception and don't create a notice
             add_chat_message(
                 user,
@@ -98,6 +97,7 @@ async def nojs_submit_message(user):
             notice, *_ = e.args
             state_id = add_state(user, notice=notice)
         else:
+            deverify(user)
             state_id = None
 
     return redirect(url_for(
diff --git a/anonstream/user.py b/anonstream/user.py
index 9c3197f..fa07cfb 100644
--- a/anonstream/user.py
+++ b/anonstream/user.py
@@ -131,3 +131,19 @@ def verify(user, digest, answer):
                 verification_happened = True
 
     return verification_happened
+
+@with_timestamp
+def deverify(timestamp, user):
+    if not user['verified']:
+        return
+
+    n_user_messages = 0
+    for message in reversed(MESSAGES):
+        message_sent_ago = timestamp - message['timestamp']
+        if message_sent_ago >= CONFIG['FLOOD_DURATION']:
+            break
+        elif message['token'] == user['token']:
+            n_user_messages += 1
+
+    if n_user_messages >= CONFIG['FLOOD_THRESHOLD']:
+        user['verified'] = False
diff --git a/anonstream/websocket.py b/anonstream/websocket.py
index 495e3f2..686b4dc 100644
--- a/anonstream/websocket.py
+++ b/anonstream/websocket.py
@@ -3,9 +3,9 @@ import asyncio
 from quart import current_app, websocket
 
 from anonstream.stream import get_stream_title, get_stream_uptime
-from anonstream.captcha import get_random_captcha_digest
+from anonstream.captcha import get_random_captcha_digest_for
 from anonstream.chat import get_all_messages_for_websocket, add_chat_message, Rejected
-from anonstream.user import get_all_users_for_websocket, see, verify, BadCaptcha
+from anonstream.user import get_all_users_for_websocket, see, verify, deverify, BadCaptcha
 from anonstream.utils.chat import generate_nonce
 from anonstream.utils.websocket import parse_websocket_data, Malformed
 
@@ -24,7 +24,7 @@ async def websocket_outbound(queue, user):
             False: CONFIG['DEFAULT_ANON_NAME'],
         },
         'scrollback': CONFIG['MAX_CHAT_SCROLLBACK'],
-        'digest': None if user['verified'] else get_random_captcha_digest(),
+        'digest': get_random_captcha_digest_for(user),
     }
     await websocket.send_json(payload)
     while True:
@@ -51,7 +51,7 @@ async def websocket_inbound(queue, user):
                 payload = {
                     'type': 'captcha',
                     'notice': notice,
-                    'digest': get_random_captcha_digest(),
+                    'digest': get_random_captcha_digest_for(user),
                 }
             else:
                 try:
@@ -63,9 +63,11 @@ async def websocket_inbound(queue, user):
                         'notice': notice,
                     }
                 else:
+                    deverify(user)
                     payload = {
                         'type': 'ack',
                         'nonce': nonce,
                         'next': generate_nonce(),
+                        'digest': get_random_captcha_digest_for(user),
                     }
         queue.put_nowait(payload)
diff --git a/config.toml b/config.toml
index 02b8b7d..b5cc138 100644
--- a/config.toml
+++ b/config.toml
@@ -35,6 +35,10 @@ max_name_length = 24
 min_name_contrast = 3.0
 background_color = "#232327"
 
+[flood]
+duration = 20
+threshold = 4
+
 [thresholds]
 user_notwatching = 8
 user_tentative = 20