diff --git a/opal/mca/btl/tcp/btl_tcp_component.c b/opal/mca/btl/tcp/btl_tcp_component.c
index 529c6eafb0..120abee313 100644
--- a/opal/mca/btl/tcp/btl_tcp_component.c
+++ b/opal/mca/btl/tcp/btl_tcp_component.c
@@ -1300,11 +1300,62 @@ static void mca_btl_tcp_component_recv_handler(int sd, short flags, void* user)
     opal_socklen_t addr_len = sizeof(addr);
     mca_btl_tcp_proc_t* btl_proc;
     int retval;
+    char str[128];
+    size_t len = strlen(mca_btl_tcp_magic_id_string);
 
     OBJ_RELEASE(event);
 
+    /* Receive the magic string */
+    assert(len < sizeof(str));
+    str[0] = '\0';
+    /* TODO: recv_blocking() will block forever, without timeout
+     * There is chance of spin forever if it tries to connect to old version
+     * as older version will send just process id which won't be long enough
+     * to cross sizeof(str) length. Probably better to have a timeout
+     * (say, 10 seconds) for receiving the magic string, and giving up after that.
+     * Will be reiterating this logic in my next iteration
+     */
+    retval = mca_btl_tcp_recv_blocking(sd, str, len);
+    if (retval > 0) {
+        str[retval] = '\0';
+    }
+
+    /* An unknown process attempted to connect to Open MPI via TCP.
+     * Open MPI uses a "magic" string to trivially verify that the connecting
+     * process is a fellow Open MPI process.  An MPI process accepted a TCP
+     * connection but did not receive the correct magic string.  This might
+     * indicate an Open MPI version mismatch between different MPI processes
+     * in the same job, or it may indicate that some other agent is
+     * mistakenly attempting to connect to Open MPI's TCP listening sockets.
+
+     * This attempted connection will be ignored; your MPI job may or may not
+     * continue properly.
+     */
+    if (retval != (int) len) {
+        opal_output_verbose(20, opal_btl_base_framework.framework_output,
+                            "server did not receive magic string. "
+                            "Local_host:%s PID:%d Role:%s String_received:%s Test_fail:%s",
+                            opal_process_info.nodename,
+                            getpid(), "server",
+                            (len > 0) ? str : "<nothing>", "string length");
+
+        /* The other side probably isn't OMPI, so just hang up */
+        CLOSE_THE_SOCKET(sd);
+        return;
+    }
+    if (0 != strncmp(str, mca_btl_tcp_magic_id_string, len)) {
+        opal_output_verbose(20, opal_btl_base_framework.framework_output,
+                            "server did not receive right magic string. "
+                            "Local_host:%s PID:%d Role:%s String_received:%s Test_fail:%s",
+                            opal_process_info.nodename,
+                            getpid(), "server", str,
+                            "string value");
+        /* The other side probably isn't OMPI, so just hang up */
+        CLOSE_THE_SOCKET(sd);
+        return;
+    }
     /* recv the process identifier */
-    retval = recv(sd, (char *)&guid, sizeof(guid), 0);
+    retval = mca_btl_tcp_recv_blocking(sd, (char *)&guid, sizeof(guid));
     if(retval != sizeof(guid)) {
         CLOSE_THE_SOCKET(sd);
         return;
diff --git a/opal/mca/btl/tcp/btl_tcp_endpoint.c b/opal/mca/btl/tcp/btl_tcp_endpoint.c
index a5ab5d50c9..f8e9ab5b8c 100644
--- a/opal/mca/btl/tcp/btl_tcp_endpoint.c
+++ b/opal/mca/btl/tcp/btl_tcp_endpoint.c
@@ -62,6 +62,10 @@
 #include "btl_tcp_frag.h"
 #include "btl_tcp_addr.h"
 
+/*
+ * Magic ID string send during connect/accept handshake
+ */
+const char mca_btl_tcp_magic_id_string[] = "OPAL-TCP-BTL";
 
 /*
  * Initialize state of the endpoint instance.
@@ -393,9 +397,24 @@ mca_btl_tcp_endpoint_send_blocking(mca_btl_base_endpoint_t* btl_endpoint,
 
 static int mca_btl_tcp_endpoint_send_connect_ack(mca_btl_base_endpoint_t* btl_endpoint)
 {
-    /* send process identifier to remote endpoint */
+
     opal_process_name_t guid = opal_proc_local_get()->proc_name;
 
+    int len = (int) strlen(mca_btl_tcp_magic_id_string);
+
+    /* send magic string to the remote endpoint, identifying me as a
+       fellow Open MPI TCP BTL */
+    if (mca_btl_tcp_endpoint_send_blocking(btl_endpoint,
+                                           mca_btl_tcp_magic_id_string,
+                                           len) != len) {
+        opal_show_help("help-mpi-btl-tcp.txt", "client handshake fail",
+                       true, opal_process_info.nodename,
+                       getpid(),
+                       "failed to send magic ID string");
+        return OPAL_ERR_UNREACH;
+    }
+
+    /* send process identifier to remote endpoint */
     OPAL_PROCESS_NAME_HTON(guid);
     if(mca_btl_tcp_endpoint_send_blocking(btl_endpoint, &guid, sizeof(guid)) !=
           sizeof(guid)) {
@@ -572,12 +591,39 @@ static int mca_btl_tcp_endpoint_recv_blocking(mca_btl_base_endpoint_t* btl_endpo
  *  Receive the endpoints globally unique process identification from a newly
  *  connected socket and verify the expected response. If so, move the
  *  socket to a connected state.
+ *
+ *  NOTE: The return codes from this function are checked in
+ *  mca_btl_tcp_endpoint_recv_handler().  Don't change them here
+ *  without also changing the handling in _recv_handler()!
  */
 static int mca_btl_tcp_endpoint_recv_connect_ack(mca_btl_base_endpoint_t* btl_endpoint)
 {
-    size_t s;
+    size_t s, len = strlen(mca_btl_tcp_magic_id_string);;
     opal_process_name_t guid;
     mca_btl_tcp_proc_t* btl_proc = btl_endpoint->endpoint_proc;
+    char msg[1024];
+
+    /* First get magic string indicating that the connector is an Open MPI TCP BTL */
+    assert(len < sizeof(msg));
+    msg[0] = '\0';
+    s = mca_btl_tcp_endpoint_recv_blocking(btl_endpoint, msg, len);
+    if (s > 0) {
+        msg[s] = '\0';
+    }
+    if (s != len) {
+        opal_show_help("help-mpi-btl-tcp.txt", "did not receive magic string",
+                       true, opal_process_info.nodename,
+                       getpid(), "client",
+                       (s > 0) ? msg : "<nothing>", "string length");
+        return OPAL_ERR_BAD_PARAM;
+    }
+    if (0 != strncmp(msg, mca_btl_tcp_magic_id_string, len)) {
+        opal_show_help("help-mpi-btl-tcp.txt", "did not receive magic string",
+                       true, opal_process_info.nodename,
+                       getpid(), "client", msg,
+                       "string value");
+        return OPAL_ERR_BAD_PARAM;
+    }
 
     s = mca_btl_tcp_endpoint_recv_blocking(btl_endpoint,
                                            &guid, sizeof(opal_process_name_t));
diff --git a/opal/mca/btl/tcp/btl_tcp_endpoint.h b/opal/mca/btl/tcp/btl_tcp_endpoint.h
index 5e40551191..77f3033bbc 100644
--- a/opal/mca/btl/tcp/btl_tcp_endpoint.h
+++ b/opal/mca/btl/tcp/btl_tcp_endpoint.h
@@ -75,6 +75,9 @@ typedef struct mca_btl_base_endpoint_t mca_btl_base_endpoint_t;
 typedef mca_btl_base_endpoint_t  mca_btl_tcp_endpoint_t;
 OBJ_CLASS_DECLARATION(mca_btl_tcp_endpoint_t);
 
+/* Magic socket handshake string */
+extern const char mca_btl_tcp_magic_id_string[];
+
 void mca_btl_tcp_set_socket_options(int sd);
 void mca_btl_tcp_endpoint_close(mca_btl_base_endpoint_t*);
 int  mca_btl_tcp_endpoint_send(mca_btl_base_endpoint_t*, struct mca_btl_tcp_frag_t*);