diff --git a/checkin_notes b/checkin_notes
index 5fcd40181f..6d0b05c1d9 100755
--- a/checkin_notes
+++ b/checkin_notes
@@ -11650,3 +11650,27 @@ Rom    April 15 2004
 
     client/
         cpu_benchmark.h
+
+David  April 18 2004
+    - Added cross-project identification (scheme developed by Janus Kristensen)
+
+    NOTE: this involves a database change (new field in user table).
+    You must update your database by adding the field and initializing it
+    (see html/ops/db_update.php) before using this code.
+
+    client/
+        client_types.C,h
+        cs_scheduler.C
+    db/
+        boinc_db.C,h
+        schema.sql
+    html/
+        user/
+            create_account_action.php
+        ops/
+            db_update.php (new)
+    py/Boinc/
+        database.py
+    sched/
+        db_dump.C
+        server_types.C
diff --git a/client/client_types.C b/client/client_types.C
index d80b80c42a..f96e8e10b9 100644
--- a/client/client_types.C
+++ b/client/client_types.C
@@ -52,6 +52,8 @@ void PROJECT::init() {
     strcpy(project_name, "");
     strcpy(user_name, "");
     strcpy(team_name, "");
+    strcpy(email_hash, "");
+    strcpy(cross_project_id, "");
     user_total_credit = 0;
     user_expavg_credit = 0;
     user_create_time = 0;
@@ -268,6 +270,8 @@ int PROJECT::parse_state(FILE* in) {
     strcpy(project_name, "");
     strcpy(user_name, "");
     strcpy(team_name, "");
+    strcpy(email_hash, "");
+    strcpy(cross_project_id, "");
     resource_share = 100;
     exp_avg_cpu = 0;
     exp_avg_mod_time = 0;
@@ -287,6 +291,8 @@ int PROJECT::parse_state(FILE* in) {
         else if (parse_str(buf, "<project_name>", project_name, sizeof(project_name))) continue;
         else if (parse_str(buf, "<user_name>", user_name, sizeof(user_name))) continue;
         else if (parse_str(buf, "<team_name>", team_name, sizeof(team_name))) continue;
+        else if (parse_str(buf, "<email_hash>", email_hash, sizeof(email_hash))) continue;
+        else if (parse_str(buf, "<cross_project_id>", cross_project_id, sizeof(cross_project_id))) continue;
         else if (parse_double(buf, "<user_total_credit>", user_total_credit)) continue;
         else if (parse_double(buf, "<user_expavg_credit>", user_expavg_credit)) continue;
         else if (parse_int(buf, "<user_create_time>", (int &)user_create_time)) continue;
@@ -339,6 +345,8 @@ int PROJECT::write_state(FILE* out) {
         "    <project_name>%s</project_name>\n"
         "    <user_name>%s</user_name>\n"
         "    <team_name>%s</team_name>\n"
+        "    <email_hash>%s</email_hash>\n"
+        "    <cross_project_id>%s</cross_project_id>\n"
         "    <user_total_credit>%f</user_total_credit>\n"
         "    <user_expavg_credit>%f</user_expavg_credit>\n"
         "    <user_create_time>%d</user_create_time>\n"
@@ -357,6 +365,8 @@ int PROJECT::write_state(FILE* out) {
         project_name,
         u2.c_str(),
         t2.c_str(),
+        email_hash,
+        cross_project_id,
         user_total_credit,
         user_expavg_credit,
         user_create_time,
@@ -391,6 +401,8 @@ void PROJECT::copy_state_fields(PROJECT& p) {
     safe_strcpy(project_name, p.project_name);
     safe_strcpy(user_name, p.user_name);
     safe_strcpy(team_name, p.team_name);
+    safe_strcpy(email_hash, p.email_hash);
+    safe_strcpy(cross_project_id, p.cross_project_id);
     user_total_credit = p.user_total_credit;
     user_expavg_credit = p.user_expavg_credit;
     user_create_time = p.user_create_time;
diff --git a/client/client_types.h b/client/client_types.h
index fa963b5289..b0d33b2897 100644
--- a/client/client_types.h
+++ b/client/client_types.h
@@ -32,6 +32,7 @@
 #include <sys/time.h>
 #endif
 
+#include "md5_file.h"
 #include "hostinfo.h"
 #include "result_state.h"
 
@@ -137,6 +138,8 @@ public:
     char project_name[256];             // descriptive.  not unique
     char user_name[256];
     char team_name[256];
+    char email_hash[MD5_LEN];
+    char cross_project_id[MD5_LEN];
     double user_total_credit;    // as reported by server
     double user_expavg_credit;    // as reported by server
     unsigned int user_create_time;   // as reported by server
diff --git a/client/cs_scheduler.C b/client/cs_scheduler.C
index f700ef5eb1..d5114a3046 100644
--- a/client/cs_scheduler.C
+++ b/client/cs_scheduler.C
@@ -293,9 +293,8 @@ int CLIENT_STATE::remove_trickle_files(PROJECT* project) {
     return 0;
 }
 
-// Prepare the scheduler request.  This writes the request in XML to a
-// file (SCHED_OP_REQUEST_FILE) which is later sent to the scheduling
-// server
+// Prepare the scheduler request.  This writes the request to a
+// file (SCHED_OP_REQUEST_FILE) which is later sent to the scheduling server
 //
 int CLIENT_STATE::make_scheduler_request(PROJECT* p, double work_req) {
     FILE* f = boinc_fopen(SCHED_OP_REQUEST_FILE, "wb");
@@ -303,6 +302,7 @@ int CLIENT_STATE::make_scheduler_request(PROJECT* p, double work_req) {
     RESULT* rp;
     int retval;
     double size;
+    char cross_project_id[MD5_LEN];
 
     if (!f) return ERR_FOPEN;
     fprintf(f,
@@ -351,6 +351,20 @@ int CLIENT_STATE::make_scheduler_request(PROJECT* p, double work_req) {
         }
     }
 
+    // send the maximum of cross_project_id over projects
+    // with the same email hash as this one
+    //
+    strcpy(cross_project_id, p->cross_project_id);
+    for (i=0; i<projects.size(); i++ ) {
+        PROJECT* project = projects[i];
+        if (project == p) continue;
+        if (strcmp(project->email_hash, p->email_hash)) continue;
+        if (strcmp(project->cross_project_id, cross_project_id) > 0) {
+            strcpy(cross_project_id, project->cross_project_id);
+        }
+    }
+    fprintf(f, "<cross_project_id>%s</cross_project_id>\n", cross_project_id);
+
     fprintf(f, "<projects>\n");
     for (i=0; i<projects.size(); i++ ) {
         PROJECT* project = projects[i];
diff --git a/db/boinc_db.C b/db/boinc_db.C
index 60bee3da35..4bd91f2fc5 100644
--- a/db/boinc_db.C
+++ b/db/boinc_db.C
@@ -209,7 +209,8 @@ void DB_USER::db_print(char* buf){
         "teamid=%d, venue='%s', url='%s', send_email=%d, show_hosts=%d, "
         "posts=%d, "
         "seti_id=%d, seti_nresults=%d, seti_last_result_time=%d, "
-        "seti_total_cpu=%.15e, signature='%s', has_profile=%d",
+        "seti_total_cpu=%.15e, signature='%s', has_profile=%d, "
+        "cross_project_id='%s'",
         id, create_time, email_addr, name,
         authenticator,
         country, postal_code,
@@ -218,7 +219,8 @@ void DB_USER::db_print(char* buf){
         teamid, venue, url, send_email, show_hosts,
         posts,
         seti_id, seti_nresults, seti_last_result_time,
-        seti_total_cpu, signature, has_profile
+        seti_total_cpu, signature, has_profile,
+        cross_project_id
     );
     UNESCAPE(email_addr);
     UNESCAPE(name);
@@ -257,6 +259,7 @@ void DB_USER::db_parse(MYSQL_ROW &r) {
     seti_total_cpu = safe_atof(r[i++]);
     strcpy2(signature, r[i++]);
     has_profile = atoi(r[i++]);
+    strcpy2(cross_project_id, r[i++]);
 }
 
 void DB_TEAM::db_print(char* buf){
diff --git a/db/boinc_db.h b/db/boinc_db.h
index 9c54a4dbed..fa3c77b254 100755
--- a/db/boinc_db.h
+++ b/db/boinc_db.h
@@ -173,6 +173,7 @@ struct USER {
     double seti_total_cpu;          // number of CPU seconds
     char signature[256];
     bool has_profile;
+    char cross_project_id[256];
     void clear();
 };
 
diff --git a/db/schema.sql b/db/schema.sql
index 26e521137d..d25006d1bf 100644
--- a/db/schema.sql
+++ b/db/schema.sql
@@ -56,7 +56,7 @@ create table app_version (
     platformid          integer     not null,
     xml_doc             blob,
     min_core_version    integer     not null,
-    max_core_version     integer    not null,
+    max_core_version    integer     not null,
     deprecated          integer     not null,
     primary key (id)
 );
@@ -86,6 +86,7 @@ create table user (
     seti_total_cpu      double      not null,
     signature           varchar(254),
     has_profile         smallint    not null,
+    cross_project_id    varchar(254) not null,
     primary key (id)
 );
 
diff --git a/html/ops/db_update.php b/html/ops/db_update.php
new file mode 100644
index 0000000000..0c9238765a
--- /dev/null
+++ b/html/ops/db_update.php
@@ -0,0 +1,20 @@
+#! /usr/local/bin/php
+<?php
+
+// code for one-time database updates goes here.
+// Don't run this unless you know what you're doing!
+
+require_once("../inc/util.inc");
+
+function update_4_18_2004() {
+    mysql_query("alter table user add cross_project_id varchar(254) not null");
+    $result = mysql_query("select * from user");
+    while ($user = mysql_fetch_object($result)) {
+        $x = random_string();
+        mysql_query("update user set cross_project_id='$x' where id=$user->id");
+    }
+}
+
+update_4_18_2004();
+
+?>
diff --git a/html/user/create_account_action.php b/html/user/create_account_action.php
index dc2e12ff15..3ad673f81a 100644
--- a/html/user/create_account_action.php
+++ b/html/user/create_account_action.php
@@ -64,9 +64,10 @@ function show_error($str) {
     }
 
     $authenticator = random_string();
+    $cross_project_id = random_string();
     $munged_email_addr = munge_email_addr($new_email_addr, $authenticator);
     $query = sprintf(
-       "insert into user (create_time, email_addr, name, authenticator, country, postal_code, total_credit, expavg_credit, expavg_time, project_prefs, teamid, venue, url, send_email, show_hosts) values(%d, '%s', '%s', '%s', '%s', '%s', 0, 0, 0, '$project_prefs', $teamid, 'home', '', 1, 1)",
+       "insert into user (create_time, email_addr, name, authenticator, country, postal_code, total_credit, expavg_credit, expavg_time, project_prefs, teamid, venue, url, send_email, show_hosts, cross_project_id) values(%d, '%s', '%s', '%s', '%s', '%s', 0, 0, 0, '$project_prefs', $teamid, 'home', '', 1, 1, $cross_project_id)",
         time(),
         $munged_email_addr,
         $new_name,
diff --git a/py/Boinc/database.py b/py/Boinc/database.py
index dd51bdd544..dcc14642db 100644
--- a/py/Boinc/database.py
+++ b/py/Boinc/database.py
@@ -102,7 +102,8 @@ class User(DatabaseObject):
                     'seti_last_result_time',
                     'seti_total_cpu',
                     'signature',
-                    'has_profile'
+                    'has_profile',
+                    'cross_project_id'
                     ])
 
 class Team(DatabaseObject):
diff --git a/sched/db_dump.C b/sched/db_dump.C
index fae3172024..7758e2124f 100644
--- a/sched/db_dump.C
+++ b/sched/db_dump.C
@@ -61,6 +61,7 @@
 
 #include "boinc_db.h"
 #include "util.h"
+#include "md5_file.h"
 #include "parse.h"
 
 #include "sched_config.h"
@@ -272,12 +273,17 @@ void write_host(HOST& host, FILE* f, bool detail, bool show_user) {
 
 void write_user(USER& user, FILE* f, bool detail, bool show_team) {
     DB_HOST host;
-    char buf[256];
+    char buf[1024];
+    char cpid[MD5_LEN];
 
     string name, url;
     xml_escape(user.name, name);
     xml_escape(user.url, url);
 
+    strcpy(buf, user.cross_project_id);
+    strcat(buf, user.email_addr);
+    md5_block((unsigned char*)buf, strlen(buf), cpid);
+
     fprintf(f,
         "<user>\n"
         " <id>%d</id>\n"
@@ -286,14 +292,16 @@ void write_user(USER& user, FILE* f, bool detail, bool show_team) {
         " <country>%s</country>\n"
         " <create_time>%d</create_time>\n"
         " <total_credit>%f</total_credit>\n"
-        " <expavg_credit>%f</expavg_credit>\n",
+        " <expavg_credit>%f</expavg_credit>\n"
+        " <cpid>%s</cpid>\n",
         user.id,
         name.c_str(),
         url.c_str(),
         user.country,
         user.create_time,
         user.total_credit,
-        user.expavg_credit
+        user.expavg_credit,
+        cpid
     );
     if (show_team) {
         fprintf(f,
diff --git a/sched/server_types.C b/sched/server_types.C
index 1c7c0a683d..fb6e7c9c68 100644
--- a/sched/server_types.C
+++ b/sched/server_types.C
@@ -26,6 +26,7 @@ using namespace std;
 #include <assert.h>
 
 #include "parse.h"
+#include "md5_file.h"
 #include "error_numbers.h"
 #include "util.h"
 #include "main.h"
@@ -175,6 +176,7 @@ int SCHEDULER_REPLY::write(FILE* fout) {
     unsigned int i, j;
     string u1, u2, t1, t2;
     int retval;
+    char email_hash[MD5_LEN];
 
     fprintf(fout,
         "<scheduler_reply>\n"
@@ -199,6 +201,7 @@ int SCHEDULER_REPLY::write(FILE* fout) {
 
     u1 = user.name;
     xml_escape(u1, u2);
+    md5_block((unsigned char*)user.email_addr, strlen(user.email_addr), email_hash);
     fprintf(fout,
         "<user_name>%s</user_name>\n"
         "<user_total_credit>%f</user_total_credit>\n"
@@ -206,14 +209,18 @@ int SCHEDULER_REPLY::write(FILE* fout) {
         "<user_create_time>%d</user_create_time>\n"
         "<host_total_credit>%f</host_total_credit>\n"
         "<host_expavg_credit>%f</host_expavg_credit>\n"
-        "<host_venue>%s</host_venue>\n",
+        "<host_venue>%s</host_venue>\n"
+        "<email_hash>%s</email_hash>\n"
+        "<cross_project_id>%s</cross_project_id>\n",
         u2.c_str(),
         user.total_credit,
         user.expavg_credit,
         user.create_time,
         host.total_credit,
         host.expavg_credit,
-        host.venue
+        host.venue,
+        email_hash,
+        user.cross_project_id
     );
 
     // might want to send team credit too.