diff --git a/common/ruletypes.h b/common/ruletypes.h
index a4a199400..60560345e 100644
--- a/common/ruletypes.h
+++ b/common/ruletypes.h
@@ -340,6 +340,9 @@ RULE_STRING(World, Rules, "", "Server Rules, change from empty to have this be u
 RULE_BOOL(World, EnableAutoLogin, false, "Enables or disables auto login of characters, allowing people to log characters in directly from loginserver to ingame")
 RULE_BOOL(World, EnablePVPRegions, true, "Enables or disables PVP Regions automatically setting your PVP flag")
 RULE_STRING(World, SupportedClients, "", "Comma-delimited list of clients to restrict to. Supported values are Titanium | SoF | SoD | UF | RoF | RoF2. Example: Titanium,RoF2")
+RULE_STRING(World, CustomFilesKey, "", "Enable if the server requires custom files and sends a key to validate. Empty string to disable. Example: eqcustom_v1")
+RULE_STRING(World, CustomFilesUrl, "github.com/knervous/eqnexus/releases", "URL to display at character select if client is missing custom files")
+RULE_INT(World, CustomFilesAdminLevel, 20, "Admin level at which custom file key is not required when CustomFilesKey is specified")
 RULE_CATEGORY_END()
 
 RULE_CATEGORY(Zone)
diff --git a/world/client.cpp b/world/client.cpp
index a6f5cfb5f..1c4b61632 100644
--- a/world/client.cpp
+++ b/world/client.cpp
@@ -541,6 +541,17 @@ bool Client::HandleSendLoginInfoPacket(const EQApplicationPacket *app)
 					skip_char_info = true;
 				}
 			}
+			const auto& custom_files_key = RuleS(World, CustomFilesKey);
+			if (!skip_char_info && !custom_files_key.empty() && cle->Admin() < RuleI(World, CustomFilesAdminLevel)) {
+				// Modified clients can utilize this unused block in login_info to send custom payloads on login
+				// which indicates they are using custom client files with the correct version, based on key payload.
+				const auto client_key = std::string(reinterpret_cast<char*>(login_info->unknown064));
+				if (custom_files_key != client_key) {
+					std::string message = fmt::format("Missing Files [{}]", RuleS(World, CustomFilesUrl) );
+					SendUnsupportedClientPacket(message);
+					skip_char_info = true;
+				}
+			}
 
 			if (!skip_char_info) {
 				SendExpansionInfo();