I’ve had this problem since yesterday.
When I attempt to download new definitions, nothing is happening for a while. Then after cca 4 minutes, it gives me an error - host unreachable. It says the definitions are up to date, but clearly they are not (they are 2 days old - 140410-0).
This is the first time I’ve encountered this problem. Firewall or any other security software isn’t blocking the access.
Thanks for any help.
do you recive stream updates?
Yes, I believe I do. They are enabled if that is what you’re asking.
Edit: I’m an idiot. Yes, I do receive them.
“C:\Program Files\AVAST Software\Avast\defs\14041200_stream” are the newest ones.
Well, tried repairing Avast, but the result remains the same.
U mě dnes naprosto stejný problém koukám je nás více…
A lot of people seem to be experiencing the same issue.
Which version of avast are you using?
2014.9.0.2016
Download and run: http://files.avast.com/ivps9x/vpsupd.exe
Thank you, the definitions seem to be up to date (140412-1).
The problem remains though, still am getting the error message when I try to update via the client.
Seems like I will have to download updates manually and then install them. 
If the problem persist, you could try the latest beta.
→ http://forum.avast.com/index.php?topic=148633.0
Not sure if that wouldn’t be worse, in the current beta there is a bug (I believe it will be fixed in the next beta update), where the streaming updates aren’t working or wait for the next beta refresh. I feel it is better to be getting these than the issue with host unreachable when doing manual virus definitions update.
So, what do you recommend? Wait and download and install the definitions manually in the meanwhile? Already tried repairing it, certainly don’t want re-installing it. I’m afraid it would do more harm than good.
Well you say the Repair and Downloading the full virus definitions database didn’t resolve it. The next step in progression would be a clean reinstall, but you say you want to avoid that. Which leaves the status quo and use the full virus definitions database database.
Having gone over the whole topic (as primarily I was only responding to Asyn’s post), are you allowing the program to auto update the virus definitions ?
If so are you getting any errors with that also or just on manual attempts ?
What does your defs folder look like (the sub-folder names are similar to the virus definition version), a little earlier mine was like this (see image) ?
Yes, the virus definitions are set to be updated automatically. The problem is they haven’t updated themselves since yesterday.
The only way I can update them is by downloading them from the link posted earlier and then installing them manually. Clicking on “Update” in the client or waiting for them to update themselves automatically doesn’t work.
I wouldn’t be opposed to a clean re-install, but it didn’t work for people experiencing the same problem.
My folder:
Well, at least updating via vpsupd.exe is still working. Didn’t work in the morning, but works now.
I have the same problem and I am using avast free 2014. It said last update received today but my definition version was from 17 april and it got stuck to that date.
I downloaded vpsupd.exe and now my definitions updated to may 8th. I think I will keep avast for now and update it every now and than with vpsupd till the problem is fixed.
Btw I repaired avast few times, reinstalled with avast deleting tool but it didn’t help.
Why not just try a clean install of the latest version to see if that fixes anything? You could download aswclear, run it, reboot, and clean install the latest Avast version. This would only take about 10 minutes of your time. I apologize if you have tried this already.