I’ve just updated avast! free to v7.0 and I cannot boot past the blue screen at start-up and the only way to get past it is to power off via the power button, restart in Safe Boot and uninstall avast.
Is this a problem experienced by others or is it just me - and what advice can anyone give to resolve this and reinstall avast! correctly?
Thanks.
Edit: I should have added that I am running a 27: quad-core i7 iMac under MacOSX.6.8, apologies.
This is for sure not a standard avast! update scenario 
Please try installing the latest version from “scratch” using the installation dmg found here:
http://download.ff.avast.com/mac/avast_free_antivirus_mac_setup.dmg
If it does not solve the issue, than look into the system log (/var/log/system.log) for avast error messages and post them here. If you find a Kernel or an avast component crashreport on your system, then please attach it to the post.