updated for version 7.3.070
Problem:    Can set environment variables in the sandbox, could be abused.
Solution:   Disallow it.
diff --git a/src/eval.c b/src/eval.c
index 7c3abf1..3564617 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -2326,7 +2326,7 @@
 	    else if (endchars != NULL
 			     && vim_strchr(endchars, *skipwhite(arg)) == NULL)
 		EMSG(_(e_letunexp));
-	    else
+	    else if (!check_secure())
 	    {
 		c1 = name[len];
 		name[len] = NUL;