Update README.md

Author: rxtur

README.md

@@ -66,7 +66,7 @@ Steps:
   5. Username: `admin` Password `admin`
 
 ### 3. Security Update
-After install, update `machineKey` in `Web.config` with values generated with tool [like this](https://www.allkeysgenerator.com/Random/ASP-Net-MachineKey-Generator.aspx). This will prevent authentication cookie exploit if you use default `admin` account.
+After install, update `machineKey` in `Web.config` with values generated with tool [like this](https://www.allkeysgenerator.com/Random/ASP-Net-MachineKey-Generator.aspx). This will prevent known exploit (reported Sep 2019). This only effects if you use default `admin` account.
 
 # Screenshot
 More screenshots on the [website](https://blogengine.io).