diff --git a/ChangeLog b/ChangeLog
index d604b1fa01..3b0176a51e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+Thu Sep 14 16:11:15 2006  Yukihiro Matsumoto  <matz@ruby-lang.org>
+
+	* string.c (rb_str_intern): raise SecurityError only when $SAFE
+	  level is greater than zero.  [ruby-core:08862]
+
+	* parse.y (rb_interned_p): new function to check if a string is
+	  already interned.
+
+	* string.c (str_to_id): use rb_str_intern().
+
 Thu Sep 14 14:37:45 2006  Tanaka Akira  <akr@fsij.org>
 
 	* ext/digest/lib/digest.rb (Digest::Base.file): new method.
diff --git a/intern.h b/intern.h
index e2fea30882..3c00a2bd2b 100644
--- a/intern.h
+++ b/intern.h
@@ -400,6 +400,7 @@ int rb_is_class_id(ID);
 int rb_is_local_id(ID);
 int rb_is_junk_id(ID);
 int rb_symname_p(const char*);
+int rb_sym_interned_p(VALUE);
 VALUE rb_backref_get(void);
 void rb_backref_set(VALUE);
 VALUE rb_lastline_get(void);
diff --git a/parse.y b/parse.y
index a9ad0673de..f5835dffec 100644
--- a/parse.y
+++ b/parse.y
@@ -8381,6 +8381,17 @@ rb_symname_p(const char *name)
     return *m ? Qfalse : Qtrue;
 }
 
+int
+rb_sym_interned_p(str)
+    VALUE str;
+{
+    ID id;
+
+    if (st_lookup(global_symbols.sym_id, (st_data_t)str, (st_data_t *)&id))
+	return Qtrue;
+    return Qfalse;
+}
+
 ID
 rb_intern2(const char *name, long len)
 {
diff --git a/string.c b/string.c
index 43d4f40747..be10152e97 100644
--- a/string.c
+++ b/string.c
@@ -4151,7 +4151,7 @@ rb_str_intern(VALUE s)
     if (!RSTRING_PTR(str) || RSTRING_LEN(str) == 0) {
 	rb_raise(rb_eArgError, "interning empty string");
     }
-    if (OBJ_TAINTED(str)) {
+    if (OBJ_TAINTED(str) && rb_safe_level() >= 1 && !rb_sym_interned_p(str)) {
 	rb_raise(rb_eSecurityError, "Insecure: can't intern tainted string");
     }
     id = rb_intern2(RSTRING_PTR(str), RSTRING_LEN(str));
@@ -4556,10 +4556,8 @@ sym_to_proc(VALUE sym)
 static ID
 str_to_id(VALUE str)
 {
-    if (!RSTRING_PTR(str) || RSTRING_LEN(str) == 0) {
-	rb_raise(rb_eArgError, "empty symbol string");
-    }
-    return rb_intern2(RSTRING_PTR(str), RSTRING_LEN(str));
+    VALUE sym = rb_str_intern(str);
+    return SYM2ID(sym);
 }
 
 ID