Since two days ago, I noted that AvastSvc.exe is running all the time, keeping the cpu at 50-54%. I have Windows xp professional SP3, and Avast free version 11.1.2241. Can you help me, please? 
Perform a repair and reboot 2 or 3 times.
If that doesn’t solve it, perform a clean installation of the latest avast version (or the beta) and reboot 2-3 times.
https://forum.avast.com/index.php?topic=178580.0
https://forum.avast.com/index.php?board=15.0
Thank you, Eddy,but how I do a repair? sorry, I’m not a genius :-[
start > control panel > software > avast > add/remove > repair
I repair, then I reboot 3 times. Was all fine during 10minutes, and then, again the problem.
This sounds a lot like the problem I reported here:
https://forum.avast.com/index.php?topic=179361.0
Try turning off ‘Home Network security’ (settings > tools > home network security (bottom of list) > off) and then reboot
This has fixed it for me & several others.
Thank you den t, I will try it now. 
Yes! It seems that it work, thank you very much den and eddy. 