afwServ.exe CPU load 50% and 745MB memory [AIS 7.0.1426 on Win7 x64]

I am sure this is not normal, but have no idea how to solve the problem.

Perhaps I should downgrade to Avast PRO version?

My CPU is dual core, so it takes up 50% of load.
The situation made me feel the system is freezed several times.
I have to cold boot the system without saving the opened files.

are u a new avast user?

does avast eat 50% of the CPU all the time when the pc is on for u?

do you have any other security programs installed ?
what AV did you use before installing avast ?
have you uninstalled it ?

This is a brand new installed Windows 7 x64.
But I did not turn off firewall of Windows when I install Avast 7.0.1426.

Does it matter?
Should I go and turn off windows’ firewall?

I checked another computer which is Windows XP x86 with AIS 6.0.1367.
afwServ.exe takes 0%CPU with 4MB memory.
This is satisfatory.