What features are lacking in the free edition that make it unsuitable for computers that contain private or sensitive information? I made the comparison to the Professional edition, but couldn’t see right off what the vulnerability is.
Script blocker. and for not-so-security-realated-for-PRO-only-feature is the Enhanced User interface which enables setting up automated scan response.
If you haven’t seen it already:
http://www.avast.com/eng/avast-compare-home-professional.html
As you can see, the home version differentiates from the Pro version with the features mentioned above.
One thing to remember, Script blocker does NOT work on Vista or Windows 7 when using IE with Protected Mode enabled.
Just noticed that he was asking for avast Free edition which is avast 5’s. I made the wrong reply.
Now, to get it right, most of those I know are Firewall, script Blocker, PUSH updates. The rest, I dunno.
The script blocker doesn’t only work with web based scripts, so that element isn’t browser dependant.
However, there will be a greater difference when version 5 hits the streets. The home/free version will have some improvements and additions, but the pro version will have additional functions. So we will have to see exactly what those differences will be nearer the time.
Many thanks to all of the replies. It appears that there aren’t any important features lacking in the free edition–except that it doesn’t remove viruses, it only finds them. Is that correct?
lulud
It is wrong, the free version which I have been using for over five years will remove viruses just as the Pro version would.
There are cases when a file can’t be dealt with (file in use, etc.), but these are specific issues that isn’t because of having the free version.
avast! antivirus - Versions comparison
http://www.avast.com/eng/avast-compare-home-professional.html
Sorry…already posted
No, fully wrong. The cleaning capacity is the same and the detection rate (virus database and heuristics) is the same.
lulud, they both are capable of removing viruses. The difference is with the free version, when you scan, it stops if a threat is detected and won’t resume until you select what to do with it. Essentially you have to babysit it while it scans. With the pro version you can predefine what it should do with threats and it will do it automatically. 
Some of the other companies that make a free version partially limit their detection or cleaning ability.
Not so Avast.
What is limited is mainly the automated scan and handling of same, and the other details as listed in the comparison chart.
IMO this makes Avast Home one of the best - if not the best - of the free versions. In fact it’s better than quite a few of the pay-for programs, I reckon.
These replies have been truly helpful–more so than any other forum I can think of. It speaks highly of the users of Avast!, and by reflection, of the program itself.
lulud
No problem, glad I could help.
Avast! 5 paid will be
Avast! premium = (similar to pro)
Avast! internet security = (will have firewall and antispam)
Seems that the name will be Pro instead of Premium.