After I installed the lastest version of Free AVAST (2015.10.2.2218), my system clock began to run fast. It now gains about 1 minute every hour. I have Windows XP SP3. I never had this problem before.
Is anyone else experiencing this problem?
Personally not experiencing this.
I too have never seen this problem (in the forums or personally) in relation to avast, which I have been using for over 11 years and on XP Pro SP3 OS for some considerable time (unintended pun). During all this time I have not seen any difference/inconsistency/change in the system time.
My system clock is off by a few seconds slow over a week or so, this inaccuracy has been consistent and I use a little tool (About Time) to connect and correct this. Though if I remember rightly there may well be a setting in the OS to connect with an atomic clock to keep it in sync.
There is a possibility that you may need to change the motherboard battery, that can effect the time, but I would have though it more slowing it than speeding it up (or getting the date/month/year completely wrong also).
Avast has no requirement (much less the functionality) to adjust the system clock.
Some possible things that can cause the clock not to function correctly:
- Dying/empty cmos battery.
- Dying/broken motherboard or other attached hardware.
- Installed software. Can be malware, but also legitimate software.
First thing I would do is replacing the battery.
A battery (CR2032) is only about $1 and you can replace one in +/- 10 minutes.
You may need to setup the bios again after doing so.
If you have to do so, depends on your system. (hardware)
Ofcourse first check if your system is using the CR2032 battery or another one.
Just adding, I agree with DavidR as I also have run Avast on my Dell Inspiron with XP installed that was purchase in 2001 and have never had " a Clock issue". 
What you saying is hard to believe. :o
I don’t believe it is avast but a hardware problem.
No problems here in this old desktop running XP and the new Avast.
I would suggest that you start with the most obvious which is to replace the battery.
If after doing that you till have a problem, then dig deeper.
Doing the reverse, makes no logical sense.
How did your Windows XP get fast with Avast Free Edition despite being an unsupported OS now?
??? he is asking about the system clock
Windows XP is still supported by avast and many other software vendors.
Windows XP is still supported by MS (although very limited) by Microsoft for private systems.
Windows XP is still supported by MS for companies, mainly the transition to a newer version of Windows now.
If you’re still using XP, you need this:
https://forum.avast.com/index.php?topic=19387.msg1208872#msg1208872