High CPU Usage

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On Windows XP SP3 Avast 2015.10.0.2208 uses an extreme amount of CPU usage for hours on end.  If I disable all shields then the CPU usage goes back to normal.  According to task manager AvastSvc.exe uses about 98% CPU usage.

As a result the system is pretty much stopped unless I disable the shields, the problem started with the 2015 version.

Any idea when this problem will be fixed?

[Eddy]

If something needs to be fixed depends on what avast is doing.
Start with a repair of avast.
If that doesn't solve things, perform a clean installation.

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Avast 2015 on Windows XP SP3 has also the problem that it slows SUMo down, and consumes much CPU (in my case around 50%, less than your 98%).

So maybe you have that problem because Avast has the same incompatibility with one of your background programs.

The culprit of the SUMo problem is "Scan programs when executing" of "File System Shield".
You can try disabling it temporarily to see if it is the culprit of your problem too.

If not, you can try disabling the shields one by one to narrow where the problem could be.