I've got exactly the same problem with 5.1.889. As soon as I upgraded to 889, my CPU usage (Avastsvc.exe)jumped to 50%. Went back to 5.1.864 - problem gone - back to zero. Back to 889 again - problem returns. Back to 864 for second time - problem gone. This has to be a bug, folks. Running Windows 7 Pro on a Dell Vostro 1500.