http://xorl.wordpress.com/2009/05/28/irssi-event_wallops-off-by-one-readwrite/

--- src/fe-common/irc/fe-events.c	2007-10-06 05:38:19.000000000 -0400
+++ src/fe-common/irc/fe-events.c.oden	2009-06-16 05:32:15.000000000 -0400
@@ -278,7 +278,7 @@ static void event_wallops(IRC_SERVER_REC
 
 		tmp = g_strdup(data+8);
 		len = strlen(tmp);
-		if (tmp[len-1] == 1) tmp[len-1] = '\0';
+		if (len >= 1 && tmp[len-1] == 1) tmp[len-1] = '\0';
 		printformat(server, NULL, MSGLEVEL_WALLOPS, IRCTXT_ACTION_WALLOPS, nick, tmp);
 		g_free(tmp);
 	}