Well, the avast is not designed to slow down your system performance. But if it happens then, it might possible that the auto-update is installing and hence it slows down the performance. For that, it is advisable to wait for a few seconds and check the update status and then restart your device. To know more about update status contact Avast Support UK for instant help. Toll Free: +44-0808-196-1478 Website: http://www.ukavast.co.uk/ Email: [email protected]