diff --git a/code/qcommon/files.c b/code/qcommon/files.c
index 8f4779d2..3602f810 100644
--- a/code/qcommon/files.c
+++ b/code/qcommon/files.c
@@ -200,7 +200,8 @@ or configs will never get loaded from disk!
 
 // every time a new demo pk3 file is built, this checksum must be updated.
 // the easiest way to get it is to just run the game and see what it spits out
-#define	DEMO_PAK_CHECKSUM	437558517u
+#define	DEMO_PAK0_CHECKSUM	2985612116u
+#define	PAK0_CHECKSUM				1566731103u
 
 // if this is defined, the executable positively won't work with any paks other
 // than the demo pak, even if productid is present.  This is only used for our
@@ -306,11 +307,6 @@ static char		*fs_serverReferencedPakNames[MAX_SEARCH_PATHS];		// pk3 names
 char lastValidBase[MAX_OSPATH];
 char lastValidGame[MAX_OSPATH];
 
-// productId: This file is copyright 1999 Id Software, and may not be duplicated except during a licensed installation of the full commercial version of Quake 3:Arena
-static byte fs_scrambledProductId[152] = {
-220, 129, 255, 108, 244, 163, 171, 55, 133, 65, 199, 36, 140, 222, 53, 99, 65, 171, 175, 232, 236, 193, 210, 250, 169, 104, 231, 231, 21, 201, 170, 208, 135, 175, 130, 136, 85, 215, 71, 23, 96, 32, 96, 83, 44, 240, 219, 138, 184, 215, 73, 27, 196, 247, 55, 139, 148, 68, 78, 203, 213, 238, 139, 23, 45, 205, 118, 186, 236, 230, 231, 107, 212, 1, 10, 98, 30, 20, 116, 180, 216, 248, 166, 35, 45, 22, 215, 229, 35, 116, 250, 167, 117, 3, 57, 55, 201, 229, 218, 222, 128, 12, 141, 149, 32, 110, 168, 215, 184, 53, 31, 147, 62, 12, 138, 67, 132, 54, 125, 6, 221, 148, 140, 4, 21, 44, 198, 3, 126, 12, 100, 236, 61, 42, 44, 251, 15, 135, 14, 134, 89, 92, 177, 246, 152, 106, 124, 78, 118, 80, 28, 42
-};
-
 #ifdef FS_MISSING
 FILE*		missingFiles = NULL;
 #endif
@@ -2856,66 +2852,48 @@ static void FS_Startup( const char *gameName ) {
 	Com_Printf( "%d files in pk3 files\n", fs_packFiles );
 }
 
-
 /*
 ===================
-FS_SetRestrictions
+FS_CheckPak0
 
-Looks for product keys and restricts media add on ability
-if the full version is not found
+Checks that pak0.pk3 is present and its checksum is correct
+Note: If you're building a game that doesn't depend on the
+Q3 media pak0.pk3, you'll want to remove this function
 ===================
 */
-static void FS_SetRestrictions( void ) {
+static void FS_CheckPak0( void )
+{
 	searchpath_t	*path;
-	char			*productId;
+	qboolean			foundPak0 = qfalse;
 
-	return;
+	for( path = fs_searchpaths; path; path = path->next ) {
+		if( path->pack &&
+				!Q_stricmpn( path->pack->pakBasename, "pak0", MAX_OSPATH ) ) {
+			foundPak0 = qtrue;
 
-#ifndef PRE_RELEASE_DEMO
-
-	// if fs_restrict is set, don't even look for the id file,
-	// which allows the demo release to be tested even if
-	// the full game is present
-	if ( !fs_restrict->integer ) {
-		// look for the full game id
-		FS_ReadFile( "productid.txt", (void **)&productId );
-		if ( productId ) {
-			// check against the hardcoded string
-			int		seed, i;
-
-			seed = 5000;
-			for ( i = 0 ; i < sizeof( fs_scrambledProductId ) ; i++ ) {
-				if ( ( fs_scrambledProductId[i] ^ (seed&255) ) != productId[i] ) {
-					break;
-				}
-				seed = (69069 * seed + 1);
+			if( path->pack->checksum == DEMO_PAK0_CHECKSUM ) {
+				Com_Printf( "\n\n"
+						"**************************************************\n"
+						"WARNING: It looks like you're using pak0.pk3\n"
+						"from the demo. This may work fine, but it is not\n"
+						"guaranteed or supported.\n"
+						"**************************************************\n\n\n" );
+			} else if( path->pack->checksum != PAK0_CHECKSUM ) {
+				Com_Printf( "\n\n"
+						"**************************************************\n"
+						"WARNING: pak0.pk3 is present but its checksum (%u)\n"
+						"is not correct. Please re-copy pak0.pk3 from your\n"
+						"legitimate Q3 CDROM.\n"
+						"**************************************************\n\n\n",
+						path->pack->checksum );
 			}
-
-			FS_FreeFile( productId );
-
-			if ( i == sizeof( fs_scrambledProductId ) ) {
-				return;	// no restrictions
-			}
-			Com_Error( ERR_FATAL, "Invalid product identification" );
 		}
 	}
-#endif
-	Cvar_Set( "fs_restrict", "1" );
 
-	Com_Printf( "\nRunning in restricted demo mode.\n\n" );
-
-	// restart the filesystem with just the demo directory
-	FS_Shutdown(qfalse);
-	FS_Startup( DEMOGAME );
-
-	// make sure that the pak file has the header checksum we expect
-	for ( path = fs_searchpaths ; path ; path = path->next ) {
-		if ( path->pack ) {
-			// a tiny attempt to keep the checksum from being scannable from the exe
-			if ( (path->pack->checksum ^ 0x02261994u) != (DEMO_PAK_CHECKSUM ^ 0x02261994u) ) {
-				Com_Error( ERR_FATAL, "Corrupted pak0.pk3: %u", path->pack->checksum );
-			}
-		}
+	if( !foundPak0 ) {
+		Com_Error( ERR_FATAL, "Couldn't find pak0.pk3. Check that your Q3\n"
+				"executable is in the correct place and that every file\n"
+				"in the baseq3 directory is present and readable." );
 	}
 }
 
@@ -3286,8 +3264,7 @@ void FS_InitFilesystem( void ) {
 	// try to start up normally
 	FS_Startup( BASEGAME );
 
-	// see if we are going to allow add-ons
-	FS_SetRestrictions();
+	FS_CheckPak0( );
 
 	// if we can't find default.cfg, assume that the paths are
 	// busted and error out now, rather than getting an unreadable
@@ -3323,8 +3300,7 @@ void FS_Restart( int checksumFeed ) {
 	// try to start up normally
 	FS_Startup( BASEGAME );
 
-	// see if we are going to allow add-ons
-	FS_SetRestrictions();
+	FS_CheckPak0( );
 
 	// if we can't find default.cfg, assume that the paths are
 	// busted and error out now, rather than getting an unreadable