diff --git a/blockcheck.sh b/blockcheck.sh
index 8a55dcf..0fe1736 100755
--- a/blockcheck.sh
+++ b/blockcheck.sh
@@ -348,6 +348,26 @@ check_system()
 	echo firewall type is $FWTYPE
 }
 
+zp_already_running()
+{
+	case "$UNAME" in
+		CYGWIN)
+			win_process_exists $PKTWSD
+			;;
+		*)
+			process_exists $PKTWSD || process_exists tpws
+	esac
+}
+check_already()
+{
+	echo \* checking already running zapret processes
+	if zp_already_running; then
+		echo "!!! WARNING. some zapret processes already running !!!"
+		echo "!!! WARNING. blockcheck requires all DPI bypass methods disabled !!!"
+		echo "!!! WARNING. pls stop all zapret instances that may interfere with blockcheck !!!"
+	fi
+}
+
 freebsd_module_loaded()
 {
 	# $1 - module name
@@ -1796,6 +1816,7 @@ sigsilent()
 fsleep_setup
 fix_sbin_path
 check_system
+check_already
 [ "$UNAME" = CYGWIN ] || require_root
 check_prerequisites
 trap sigint_cleanup INT
diff --git a/common/base.sh b/common/base.sh
index cdfc7d9..7c772ef 100644
--- a/common/base.sh
+++ b/common/base.sh
@@ -313,6 +313,22 @@ shell_name()
 	}
 }
 
+process_exists()
+{
+	if exists pgrep; then
+		pgrep ^$1$ >/dev/null
+	elif exists pidof; then
+		pidof $1 >/dev/null
+	else
+		return 1
+	fi 
+}
+
+win_process_exists()
+{
+	tasklist /NH /FI "IMAGENAME eq ${1}.exe" | grep -q "^${1}.exe"
+}
+
 std_ports()
 {
         HTTP_PORTS=${HTTP_PORTS:-80}