--- a/virus.rst	Mon Oct 11 17:34:50 2010 +0300
+++ b/virus.rst	Tue Oct 12 09:50:42 2010 +0300
@@ -18,17 +18,23 @@
   $ sudo chkrootkit
 ...
 
-* Virus.
+* Debian.
 
-** Debian.
-
-*** ClamAV.
+** ClamAV.
 
 anti-virus utility for Unix.
 
   $ sudo apt-get install clamav
 
-** Windows.
+* Windows.
+
+** Free.
+
+*** Microsoft Security Essentials.
+
+  http://en.wikipedia.org/wiki/Microsoft_Security_Essentials
+
+** Non free.
 
 *** Nod32.