Q: Mavericks asks for icloud password everytime on startup

Opening system preferences > iCloud.

Try updating your password here.

Hope it helps.

Run Keychain First Aid.

Open Keychain Access in Applications/Utilities

Under Keychain Access in the Menu bar select Keychain First Aid.

Enter your user name and password.

Select Repair and click Start.

If any problems are found run again to verify all repaired.

Have you updated to OS X 10.9.3? If not, let's do that first.

OS X Mavericks 10.9.3 (Update (Combo)

http://support.apple.com/kb/DL1746

If you are fully updated to OS X 10.9.3....

In your User's Library > Preferences delete com.apple.keychainaccess.plist

Log out under the Apple in the Menu bar

Did the problem go away?

If no...

Do the step here:

OS X Mavericks v10.9.1: Repeated prompts to unlock "Local Items" keychain

http://support.apple.com/kb/TS5362

Still an issue...

Reset your Keychain.

Resetting your keychain in Mac OS X

http://support.apple.com/kb/TS1544

We need to determine if it's actually missing files or you finding the files.

Let's start with finding the User's Library. See this link on how to make the User's Library folder visible.

How to enable the User’s Library folder

Did you try downloading and running the combo?

Wama103 has a very good and a very straight forward well defined question. And I have the same problem. What we are met with here is a lot of guesswork - and no real answer. Is there no way of getting Apple to explain this - and solve this - once and for all?

Besides, this window that keeps asking us for a password - how do we know it is generated by Mavericks? For a security IT technician like me, its anonymity is suspect and could just as well be presented by som hacker or virus or evil software.

For some time now - the windows started to pop up just a handful of days ago - I just cancel the windows. And nothing seems to go wrong anywhere...

Arn of Sweden

Issues like repeated prompts for password can have fixes in more than one place. Often is no one simple fix. As an IT tech you should know this.

If iCloud is prompting for a password and you ignore, then the iCloud feature will fail to connect. No harn done. I suggest you Sign Out of iCloud in System Preferences > iCloud. This should stop iCloud from asking for a password.

You are not talking to Apple here. We are users just like you that volunteer our time here to help other users.

Unless you have selected to turn off  "only allow downloads from Mac App Store and identified developers" in System Preferences > Security & Privacy you shouldn't be seeing some hacker or evil software installed on your drive.

Linc Davis' reply on virus software. This explains how your Mac helps protect you.

https://discussions.apple.com/thread/6433251

Have you tried repairing disk permissions?

"Braze Blade", the same thing has been happening to me, since I upgraded to 10.9.4 a few days ago. The message appears only when I have my internet Router turned OFF while I am logging in to the computer; not when the Router is (on the rare occasion) connected when I log in.

I believe it may be because one or more of the iCloud-authorized apps checks its internet access to iCloud at computer start up (unfortunately) rather than when the app is opened the first time, which would make more sense.  In my case, this is the Notes app.; but it could be the case with other apps. authorized (i.e. "checked") in the System Preferences > iCloud panel. 

Canceling the window is what I do also, until the router is on. Signing Out from the System Preferences Panel > iCloud screen is another option. Once logged out,  data stored on iCloud will not show up on apps (like Notes) on your Mac, until you log into iCloud again.

Because this feature is rather new, and pretty much a nag, I personally consider it a bug. Better that the iCloud login screen would first appear when we are actually accessing an app that we have authorized to connect to iCloud.

No, I have not reset disk permissions. But I am going to do it - allthough I did it only three months ago. Thanx for your suggestion. It's worth a try, though I am not quite certain that the solution to the problem is that simple. 

This kind of confirms my own assumptions. And a bug and a nag it is. Indeed. Thanx a lot for your very good answer. Much appreciated.