diff --git a/CHANGELOG.md b/CHANGELOG.md
index 172f5f7b..edfcada8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,7 @@
 - fix chromium compatibility (@caryoscelus)
 - better fix of local sites leak (@caryoscelus)
 - ipython-based repl via --repl for debug/interactive development (@caryoscelus)
+- optional blocking of compromised id certificates for spam protection (@caryoscelus)
 - various improvements
 
 ### zeronet-conservancy 0.7.10 (2023-07-26) (18d35d3bed4f0683e99)
diff --git a/src/Config.py b/src/Config.py
index ba519a6b..72e10d92 100644
--- a/src/Config.py
+++ b/src/Config.py
@@ -311,6 +311,8 @@ class Config:
 
         self.parser.add_argument('--download-optional', choices=["manual", "auto"], default="manual")
 
+        self.parser.add_argument('--lax-cert-check', action=argparse.BooleanOptionalAction, default=True, help="Enabling lax cert check allows users getting site writing priviledges by employing compromized (i.e. with leaked private keys) cert issuer. Disable for spam protection")
+
         self.parser.add_argument('--tor', help='enable: Use only for Tor peers, always: Use Tor for every connection', choices=["disable", "enable", "always"], default='enable')
         self.parser.add_argument('--tor-controller', help='Tor controller address', metavar='ip:port', default='127.0.0.1:9051')
         self.parser.add_argument('--tor-proxy', help='Tor proxy address', metavar='ip:port', default='127.0.0.1:9050')
diff --git a/src/Content/ContentManager.py b/src/Content/ContentManager.py
index a06ba523..938f3d6f 100644
--- a/src/Content/ContentManager.py
+++ b/src/Content/ContentManager.py
@@ -29,7 +29,17 @@ class SignError(Exception):
 
 
 @PluginManager.acceptPlugins
-class ContentManager(object):
+class ContentManager:
+    """Manage site content verifying and other related stuff"""
+
+    def loadBadCerts():
+        try:
+            with open(f'{config.data_dir}/badcerts.json') as f:
+                return set(json.load(f))
+        except FileNotFoundError:
+            return set()
+
+    bad_certs = loadBadCerts()
 
     def __init__(self, site):
         self.site = site
@@ -38,6 +48,13 @@ class ContentManager(object):
         self.hashfield = PeerHashfield()
         self.has_optional_files = False
 
+    def addBadCert(self, sign):
+        addr = CryptBitcoin.get_sign_address_64('compromised', sign)
+        if addr:
+            self.bad_certs.add(addr)
+            with open(f'{config.data_dir}/badcerts.json', 'w') as f:
+                json.dump(list(self.bad_certs), f)
+
     # Load all content.json files
     def loadContents(self):
         if len(self.contents) == 0:
@@ -478,6 +495,9 @@ class ContentManager(object):
                 return self.getUserContentRules(parent_content, inner_path, content)
         return False
 
+    def isGoodCert(self, cert):
+        return cert not in self.bad_certs
+
     # Get rules for a user file
     # Return: The rules of the file or False if not allowed
     def getUserContentRules(self, parent_content, inner_path, content):
@@ -511,7 +531,20 @@ class ContentManager(object):
             banned = False
         if "signers" in rules:
             rules["signers"] = rules["signers"][:]  # Make copy of the signers
-        for permission_pattern, permission_rules in list(user_contents["permission_rules"].items()):  # Regexp rules
+
+        if content is not None:
+            name, domain = content['cert_user_id'].rsplit('@', 1)
+            cert_addresses = parent_content['user_contents']['cert_signers'].get(domain)
+        else:
+            cert_addresses = None
+        # to prevent spam, if cert is compromised, only allow personal rules
+        if config.lax_cert_check or cert_addresses is None or self.isGoodCert(cert_addresses[0]):
+            permission_rules = user_contents.get('permission_rules', {}).items()
+            if not self.isGoodCert(cert_addresses[0]):
+                self.log.warning('Accepting compromised certificate! This may lead to spam attack. Turn off with --no_lax_cert_check. Default behaviour may change in the future.')
+        else:
+            permission_rules = {}
+        for permission_pattern, permission_rules in permission_rules:  # Regexp rules
             if not SafeRe.match(permission_pattern, user_urn):
                 continue  # Rule is not valid for user
             if permission_rules is None:
@@ -892,9 +925,9 @@ class ContentManager(object):
             raise VerifyError("No rules")
 
         # Check include size limit
-        if rules.get("max_size") is not None:  # Include size limit
-            if content_size > rules["max_size"]:
-                raise VerifyError("Include too large %sB > %sB" % (content_size, rules["max_size"]))
+        max_size = rules.get("max_size", 0)
+        if content_size > max_size:
+            raise VerifyError(f'Include too large {content_size}B > {max_size}B')
 
         if rules.get("max_size_optional") is not None:  # Include optional files limit
             if content_size_optional > rules["max_size_optional"]:
diff --git a/src/Crypt/CryptBitcoin.py b/src/Crypt/CryptBitcoin.py
index a0807187..25377f5d 100644
--- a/src/Crypt/CryptBitcoin.py
+++ b/src/Crypt/CryptBitcoin.py
@@ -4,6 +4,9 @@ import binascii
 import time
 import hashlib
 
+from collections.abc import Container
+from typing import Optional
+
 from util.Electrum import dbl_format
 from Config import config
 
@@ -69,7 +72,8 @@ def privatekeyToAddress(privatekey):  # Return address from private key
         return False
 
 
-def sign(data, privatekey):  # Return sign to data using private key
+def sign(data: str, privatekey: str) -> str:
+    """Sign data with privatekey, return base64 string signature"""
     if privatekey.startswith("23") and len(privatekey) > 52:
         return None  # Old style private key not supported
     return base64.b64encode(sslcurve.sign(
@@ -79,13 +83,13 @@ def sign(data, privatekey):  # Return sign to data using private key
         hash=dbl_format
     )).decode()
 
-
-def verify(data, valid_address, sign, lib_verify=None):  # Verify data using address and sign
+def get_sign_address_64(data: str, sign: str, lib_verify=None) -> Optional[str]:
+    """Returns pubkey/address of signer if any"""
     if not lib_verify:
         lib_verify = lib_verify_best
 
     if not sign:
-        return False
+        return None
 
     if lib_verify == "libsecp256k1":
         sign_address = libsecp256k1message.recover_address(data.encode("utf8"), sign).decode("utf8")
@@ -95,10 +99,23 @@ def verify(data, valid_address, sign, lib_verify=None):  # Verify data using add
     else:
         raise Exception("No library enabled for signature verification")
 
-    if type(valid_address) is list:  # Any address in the list
-        return sign_address in valid_address
-    else:  # One possible address
-        return sign_address == valid_address
+    return sign_address
+
+def verify(*args, **kwargs):
+    """Default verify, see verify64"""
+    return verify64(*args, **kwargs)
+
+def verify64(data: str, addresses: str | Container[str], sign: str, lib_verify=None) -> bool:
+    """Verify that sign is a valid signature for data by one of addresses
+
+    Expecting signature to be in base64
+    """
+    sign_address = get_sign_address_64(data, sign, lib_verify)
+
+    if isinstance(addresses, str):
+        return sign_address == addresses
+    else:
+        return sign_address in addresses
 
 def isValidAddress(addr):
     '''Check if provided address is valid bitcoin address'''
diff --git a/src/Ui/UiWebsocket.py b/src/Ui/UiWebsocket.py
index 086e4444..a87abd62 100644
--- a/src/Ui/UiWebsocket.py
+++ b/src/Ui/UiWebsocket.py
@@ -407,6 +407,9 @@ class UiWebsocket(object):
     def actionSiteBadFiles(self, to):
         return list(self.site.bad_files.keys())
 
+    def actionBadCert(self, to, sign):
+        self.site.content_manager.addBadCert(sign)
+
     # Join to an event channel
     def actionChannelJoin(self, to, channels):
         if type(channels) != list: