A few times recently the date on my computer has changed by itself. Why would this happen?

get a new battery for your motherboard

if he has XP the date is updated over the net.

That may change the time, but the date?

I thought it was updated over the net as well. Today my computer read 20/10/06 so it jumped a week. I have XP.

Virus?

I have run NOD32 Virus program and it comes up with nothing. I am also behind windows firewall and a university firewall. But maybe it still is a virus, I don't know!

How does it change? Does it jump forward? Backward? By how much? How often?

If you don't set it back again, does it keep changing (other than in the ordinary way)?

I have run NOD32 Virus program and it comes up with nothing. I am also behind windows firewall and a university firewall. But maybe it still is a virus, I don't know!

As Kunax has already pointed out - it's likely you're board battery. Replace it with a new one, see if that stops the problem.

It's difficult to say if it's jumped a week, usually if it's the onboard battery you'll either lose time or it will reset to the factory default which is usually the date of the boards creation or BIOS.

It is indeed possible that the clock/date was checked against an online timeserver which could of possibly had a different date or date format, as it doesn't just adjust time it will adjust the date too (for those lazy people that can't remember it or just don't want to go through the process of entering it by hand. Although it can be handy for Cluster installations)

It's possible (I'll check this after posting) that the Time server runs on a UDP protocol, which means that if your system is listening as a client for time syncronous data that someone could be sending a malformed packet causing your date to change wrongly, however if its TCP it's not so much of a possibility.

As for "Viruses" you'd find a program running at bootup, it would either be found in the Startup folder or found through msconfig. If it's a "Zombie server" then the likelihood is that after you bootup the program will still be running in your task list. You'd just have to identify it and kill it (If found do this before trying to disable it from starting up next boot)

[Edit]
Apparently the Time Service runs on port 123 as Symmetrical UDP (Both incoming and outgoing), Which a firewall might block creating either a loss in data or different data.

Apparently the Following fixes such time keeping problems in XP:

Go to the Run.. dialogue box found through the Start button and type CMD
This will generate the commandline environment, then type the following lines:

net stop w32time
w32tm /unregister [Ignore error messages]
w32tm /unregister [Enter a second time]
w32tm /register
net start w32time

source document: http://tf.nist.gov/service/pdf/win2000xp.pdf

Maybe you're in some sort of weird temporal rift, and your computer is keeping accurate time.

Unfortunately, it would make your question off topic, and you would have to repost in the physics and math forum.

It's difficult to say if it's jumped a week, usually if it's the onboard battery you'll either lose time or it will reset to the factory default which is usually the date of the boards creation or BIOS.

Yeah, thinking about it, that's exactly right. Sorry. Off m'game today. Superb post, btw. http://www.sciforums.com/images/icons/icon14.gif

PSEUDOSCIENCE SECTION ANSWER: The Philidelphia Project timewarped your computer ahead a week!