diff -ur zoo-2.10-r2/zooext.c zoo-2.10-r3/zooext.c
--- zoo-2.10-r2/zooext.c	2007-05-23 23:39:14.000000000 +0200
+++ zoo-2.10-r3/zooext.c	2007-05-23 23:36:37.000000000 +0200
@@ -89,6 +89,7 @@
 #endif
 struct direntry direntry;                 /* directory entry */
 int first_dir = 1;								/* first dir entry seen? */
+ unsigned long zoo_pointer = 0;           /* Track our position in the file */
 
 static char extract_ver[] = "Zoo %d.%d is needed to extract %s.\n";
 static char no_space[] = "Insufficient disk space to extract %s.\n";
@@ -169,6 +170,9 @@
 		exit_status = 1;
    }
    zooseek (zoo_file, zoo_header.zoo_start, 0); /* seek to where data begins */
+
+   /* Begin tracking our position in the file */ 
+   zoo_pointer = zoo_header.zoo_start; 
 }
 
 #ifndef PORTABLE
@@ -597,6 +601,11 @@
    } /* end if */
 
 loop_again:
+   /* Make sure we are not seeking to already processed data */ 
+   if (next_ptr <= zoo_pointer)
+     prterror ('f', "ZOO chain structure is corrupted\n");
+   zoo_pointer = next_ptr; 
+
    zooseek (zoo_file, next_ptr, 0); /* ..seek to next dir entry */
 } /* end while */
 
Nur in zoo-2.10-r3: zooext.c~.
Nur in zoo-2.10-r3: zooext.c.orig.
diff -ur zoo-2.10-r2/zoolist.c zoo-2.10-r3/zoolist.c
--- zoo-2.10-r2/zoolist.c	1991-07-20 00:57:27.000000000 +0200
+++ zoo-2.10-r3/zoolist.c	2007-05-23 23:38:19.000000000 +0200
@@ -92,7 +92,7 @@
 int show_mode = 0;				/* show file protection */
 #endif
 int first_dir = 1;				/* if first direntry -- to adjust dat_ofs */
-
+unsigned long zoo_pointer = 0; /* Track our position in the file */
 while (*option) {
    switch (*option) {
       case 'a': show_name++; break;
@@ -211,6 +211,9 @@
 		show_acmt (&zoo_header, zoo_file, 0);		/* show archive comment */
 	}
 
+	/* Begin tracking our position in the file */
+	zoo_pointer = zoo_header.zoo_start;
+
    /* Seek to the beginning of the first directory entry */
    if (zooseek (zoo_file, zoo_header.zoo_start, 0) != 0) {
       ercount++;
@@ -437,6 +440,11 @@
          if (verb_list && !fast)
             show_comment (&direntry, zoo_file, 0, (char *) NULL);
       } /* end if (lots of conditions) */
+
+      /* Make sure we are not seeking to already processed data */
+      if (direntry.next <= zoo_pointer)
+        prterror ('f', "ZOO chain structure is corrupted\n");
+      zoo_pointer = direntry.next;
    
 		/* ..seek to next dir entry */
       zooseek (zoo_file, direntry.next, 0);
Nur in zoo-2.10-r3: zoolist.c~.
Nur in zoo-2.10-r3: zoolist.c.orig.