diff -r 000000000000 -r 40cabcdcd2be samples/cloneproblem/test/org/apidesign/cloneproblem/ExploitTest.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/samples/cloneproblem/test/org/apidesign/cloneproblem/ExploitTest.java	Thu Oct 30 21:30:10 2014 +0100
@@ -0,0 +1,44 @@
+package org.apidesign.cloneproblem;
+
+import java.util.Date;
+import junit.framework.TestCase;
+
+/** Test that would be written by the API hacker.
+ *
+ * @author Jaroslav Tulach <jaroslav.tulach@apidesign.org>
+ */
+public class ExploitTest extends TestCase {
+    public ExploitTest(String name) {
+        super(name);
+    }
+
+    public void testExploitOverridableClone() {
+        try {
+            HackedDate now = new HackedDate();
+            HackedDate later = new HackedDate(now.getTime() + 1000);
+            
+            Interval interval = new Interval(now, later);
+            assertEquals("1s", 1000, interval.getLength());
+            
+            fail("And I hoped NullPointerException will be thrown!");
+        }  catch (NullPointerException ex) {
+            // success, the quest is to generate NullPointerException!
+        }
+    }
+
+    // BEGIN: interval.exploit
+    private static class HackedDate extends Date {
+        public HackedDate() {
+        }
+
+        public HackedDate(long date) {
+            super(date);
+        }
+
+        @Override
+        public Object clone() {
+            return null;
+        }
+    }
+    // END: interval.exploit
+}