diff --git a/monkey/common/network/segmentation_utils.py b/monkey/common/network/segmentation_utils.py
index 68122f398..97adbd203 100644
--- a/monkey/common/network/segmentation_utils.py
+++ b/monkey/common/network/segmentation_utils.py
@@ -10,9 +10,12 @@ def get_ip_in_src_and_not_in_dst(ip_addresses, source_subnet, target_subnet):
     :param target_subnet:   Subnet we want an IP to be in.
     :return:    The cross segment IP if in source but not in target, else None.
     """
-    for ip_address in ip_addresses:
-        if target_subnet.is_in_range(ip_address):
-            return None
+    if get_ip_if_in_subnet(ip_addresses, target_subnet) is not None:
+        return None
+    return get_ip_if_in_subnet(ip_addresses, source_subnet)
+
+
+def get_ip_if_in_subnet(ip_addresses, source_subnet):
     for ip_address in ip_addresses:
         if source_subnet.is_in_range(ip_address):
             return ip_address
diff --git a/monkey/monkey_island/cc/services/telemetry/processing/scan.py b/monkey/monkey_island/cc/services/telemetry/processing/scan.py
index 3b532ff22..8ae386388 100644
--- a/monkey/monkey_island/cc/services/telemetry/processing/scan.py
+++ b/monkey/monkey_island/cc/services/telemetry/processing/scan.py
@@ -3,11 +3,13 @@ import copy
 from monkey_island.cc.database import mongo
 from monkey_island.cc.services.telemetry.processing.utils import get_edge_by_scan_or_exploit_telemetry
 from monkey_island.cc.services.telemetry.zero_trust_tests.data_endpoints import test_open_data_endpoints
+from monkey_island.cc.services.telemetry.zero_trust_tests.segmentation import test_segmentation_violation
 
 
 def process_scan_telemetry(telemetry_json):
     update_edges_and_nodes_based_on_scan_telemetry(telemetry_json)
     test_open_data_endpoints(telemetry_json)
+    test_segmentation_violation(telemetry_json)
 
 
 def update_edges_and_nodes_based_on_scan_telemetry(telemetry_json):
diff --git a/monkey/monkey_island/cc/services/telemetry/zero_trust_tests/segmentation.py b/monkey/monkey_island/cc/services/telemetry/zero_trust_tests/segmentation.py
new file mode 100644
index 000000000..ca308aafd
--- /dev/null
+++ b/monkey/monkey_island/cc/services/telemetry/zero_trust_tests/segmentation.py
@@ -0,0 +1,68 @@
+import itertools
+from six import text_type
+
+from common.data.zero_trust_consts import STATUS_CONCLUSIVE, EVENT_TYPE_MONKEY_NETWORK
+from common.network.network_range import NetworkRange
+from common.network.segmentation_utils import get_ip_in_src_and_not_in_dst, get_ip_if_in_subnet
+from monkey_island.cc.models import Monkey
+from monkey_island.cc.models.zero_trust.event import Event
+from monkey_island.cc.models.zero_trust.segmentation_finding import SegmentationFinding
+from monkey_island.cc.services.configuration.utils import get_config_network_segments_as_subnet_groups
+
+SEGMENTATION_VIOLATION_EVENT_TEXT = \
+    "Segmentation violation! Monkey on '{hostname}', with the {source_ip} IP address (in segment {source_seg}) " \
+    "managed to communicate cross segment to {target_ip} (in segment {target_seg})."
+
+
+def is_segmentation_violation(current_monkey, target_ip, source_subnet, target_subnet):
+    if source_subnet == target_subnet:
+        return False
+    source_subnet_range = NetworkRange.get_range_obj(source_subnet)
+    target_subnet_range = NetworkRange.get_range_obj(target_subnet)
+
+    if target_subnet_range.is_in_range(text_type(target_ip)):
+        cross_segment_ip = get_ip_in_src_and_not_in_dst(
+            current_monkey.ip_addresses,
+            source_subnet_range,
+            target_subnet_range)
+
+        return cross_segment_ip is not None
+
+
+def test_segmentation_violation(telemetry_json):
+    """
+
+    :param telemetry_json: A SCAN telemetry sent from a Monkey.
+    """
+    # TODO - lower code duplication between this and report.py.
+    # TODO - single machine
+    current_monkey = Monkey.get_single_monkey_by_guid(telemetry_json['monkey_guid'])
+    target_ip = telemetry_json['data']['machine']['ip_addr']
+    subnet_groups = get_config_network_segments_as_subnet_groups()
+    for subnet_group in subnet_groups:
+        subnet_pairs = itertools.product(subnet_group, subnet_group)
+        for subnet_pair in subnet_pairs:
+            source_subnet = subnet_pair[0]
+            target_subnet = subnet_pair[1]
+            if is_segmentation_violation(current_monkey, target_ip, source_subnet, target_subnet):
+                event = get_segmentation_violation_event(current_monkey, source_subnet, target_ip, target_subnet)
+                SegmentationFinding.create_or_add_to_existing_finding(
+                    subnets=[source_subnet, target_subnet],
+                    status=STATUS_CONCLUSIVE,
+                    segmentation_event=event
+                )
+
+
+def get_segmentation_violation_event(current_monkey, source_subnet, target_ip, target_subnet):
+    return Event.create_event(
+        title="Segmentation event",
+        message=SEGMENTATION_VIOLATION_EVENT_TEXT.format(
+            hostname=current_monkey.hostname,
+            source_ip=get_ip_if_in_subnet(current_monkey.ip_addresses, NetworkRange.get_range_obj(source_subnet)),
+            source_seg=source_subnet,
+            target_ip=target_ip,
+            target_seg=target_subnet
+        ),
+        event_type=EVENT_TYPE_MONKEY_NETWORK
+    )
+