OK this is a reply to an old topic - I know - but I always /hate/ starting new topics because of the added confusion it causes, and it seems relevant to this issue as far as I can tell. ALSO: It may be that others looking for help with this issue will read through this thread first anyway. If others deem it important enough I will post it to a new topic, however for the time being I’m putting it here.
RIGHT: Firstly, I am running Avast version 5.0.462 on a laptop running XP SP2, Intel pentium 4 with 512 Mb RAM, and a SiS graphics card (ACER Aspire 1700).
Next, I was running Avast! 4 and updated, not an un/install but an upgrade.
Right, so what happens is it started up fine, the notification tray has the “a” icon (no “f” I notice BTW), and it spins around satisfyingly and Avast has all the default settings, ie: ALL scanners activated, no expert settings tweaked (bar one: I prefer to update manually as I am on dial-up, and make it part of my regular maintance schedule, so I have a regular weekly update along with all the other things like emptying temp, regular clean-up and defrag, all the usual stuff one needs to do).
NOW all that is fine up to a point. When I open the UI everything slows to a crawl and I was nearly tempted to halt and restart but found ONE WAY TO AVOID HALTING AND RESTARTING that may be of interest to others having this issue.
The computer has slowed to a crawl, so DO NOT TRY OPENING OTHER WINDOWS or other APPLICATIONS, and DO NOT CTRL+ALT+DEL to use task manager to halt the process. You will notice the mouse cursor moves, just VERY SLOWLY, so bring it down to the taskbar and onto the Avast tab - this will take a little while, just BE PATIENT and move it slowly/incrementally.
When the Avast! TAB in the taskbar changes to highlighted, CLICK IT ONCE and WAIT. This may or may not work, give it a few seconds - about twenty to maybe a minute depending on how many other processes are going on, it should minimise. If nothing happens, try once again clicking and wait, if you click a second time you may find the program (UI / window) will shrink down and raise up again. You want to minise the program to the TAB, so get the window to shrink down (ie: minimise). You should now find your mouse/desktop responds a little faster.
The point is that now you can RIGHT-CLICK on that tab and select close, or hit ALT+F4 (while the tab is highlighted obviously, otherwise you might be closing another program 
).
The point to doing this rather than using task manager is that you may avoid the problems that come with shutting down applications while they are running, corrupting files etc. It also leaves the Avast SCANNER itself still running, so you’re still protected if you’re online (fingers crossed ).
NOW: The point I want to make is that this is what I found worked for me. Your Mileage May Vary.
The other thing is that I feel that this problem /may/ have something to do with the interface that runs the graphic scrolling within each of the settings tabs (you know, the ones that update how your scanner is running and what it’s been doing etc etc. ). This may be all very well for the eye candy, but for lower power machines and perhaps those running XP and not the Vista style window decorations, it slows the interface down immensely - so much that people think their computer has crashed - I’m reminded of a famous “Furry Freak Brothers” cartoon where the cops said "These hippies rode away from us so fast we thought we’d stopped so we got out to have a look … " 
And this is really unnnnnn necesary. Sure, it looks great, and for those with the latest CPU and real high end graphics cards it’s really neat. BUT NOT EVERYONE HAS THOSE HIGH END MACHINES, and they will not buy your products if it leaves them with a poor impression.
SO PLEASE! PLEASE! PLEASE! can you make your UI so that these things aren’t on BY DEFAULT?
Of course, it might be the JAVA implementation of the window set, at a guess, but I don’t really know what windowing toolkit you used so I won’t say for what is causing the problem. What I do know is that it is a problem and can easily be dealt with with a little bit of user testing. Don’t test your software on the public at large unless you want them to badmouth your products.
So - can you enable turning off the GUI decoration - preferably without forcing XP users to choose the Windows98 styling for their desktops?
Alternatively, IF YOU HAVE THIS PROBLEM, TRY setting your desktop to the “Windows Classic Desktop” in your appearance tab under the Display Properties control panel (right-click on your desktop for quick access) - this may help you avoid the slowing down problem, or it may not. Again, YMMV. IIRC, Avast 4 still had it’s shiny interface on my other system where I do use Classic style - that machine is a PIII 128Mb so it’s actually a miracle XP runs on it at all to be perfectly honest, BUT I DIGRESS - sorry. :}
Please don’t mistake my criticisms for abuse, I actually am a fan of AVAST!, it’s been keeping my system clean for several years now, and I like shiny interfaces. I just think that they may not be for everybody and it might be nice to be able to select between a basic and a shiny interface.
OH YEAH, and can I also say really really great that you’re supporting Linux OS now… really big step that and I hope it pays off, because it’s important to support linux IMHO. ;D ;D ;D