« Reply #4 on: February 16, 2014, 01:33:28 AM »
On a Win8 system, Windows Defender should automatically disable itself when you install avast [or any other recognized anti-virus program].

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Lenovo T530 laptop, Intel Core i5-3320M @ 2.60 GHz, 8GB RAM, Windows 7 Pro SP1 (64-bit), avast! 17 Free, MBAM3 Pro, Windows Firewall, MVPS HOSTS file, OpenDNS Family Shield, Zemana AntiLogger Free, SpywareBlaster, IE11 & Firefox [both using WOT (IE set to WARN, FF set to BLOCK)], WinPatrol PLUS, uBlock Origin, MBAE, MCShield, CryptoPrevent, SAS (on-demand scanner).
[I believe computer-users who sandbox (Sandboxie) are acting prudently.]