--- tcp_input.c.orig  Tue Apr 20 15:09:15 1999
+++ tcp_input.c  Fri Jan 21 21:53:00 2000
@@ -398,12 +398,36 @@
           "Connection attempt to TCP %s:%d from %s:%d\n",
           buf, ntohs(ti->ti_dport), inet_ntoa(ti->ti_src),
           ntohs(ti->ti_sport));
-    }
+    } else if (tiflags & TH_ACK) {
+      /*
+       * Alpha code in response to stream.c
+       * - Omachonu Ogali <oogali@intranova.net>
+       */
+      char buf[4*sizeof "123"];
+
+#ifdef ICMP_BANDLIM
+      if (badport_bandlim(1) < 0)
+        goto drop;
+#endif
+
+      strcpy(buf, inet_ntoa(ti->ti_dst));
+      log(LOG_INFO,
+          "received TCP/ACK to non existant connection: %s:%d -> %s:%d\n",
+          inet_ntoa(ti->ti_src), ntohs(ti->ti_sport), buf, ntohs(ti->ti_dport));
+
+      /*
+       * Drop without reset to prevent smurf-like tcp
+       * attack
+       */
+
+      goto drop;
+    } else {
 #ifdef ICMP_BANDLIM
     if (badport_bandlim(1) < 0)
       goto drop;
 #endif
     goto dropwithreset;
+    }
   }
   tp = intotcpcb(inp);
   if (tp == 0)