Q: Little dots automatically fill the password field

You're fixating on the wrong thing. Malware (not a virus) can't be running at login, because there is no access to system resources until somebody logs in. Just because something doens't seem to work right does not mean you should leap to the thought that you have malware or a virus. There are no viruses for Mac OS X.

However, there are some questions to be posed here:

1. Who is the "administrator" of this Mac?

2. When did this issue start happening, and what software was installed just before it started happening?

3. Have you tried restoring from a working backup where this problem didn't happen?

4. If the answer t 3 is 'Yes', and it's still happening, have you tried Repair Permissions, or any other type of disk utility, such as DiskWarrior, TechTool Pro, etc.?

Malware (not a virus) can't be running at login, because there is no access to system resources until somebody logs in.

Hi Kurt, I can't say why this is happening, though I agree it's extremely unlikely to be malware. But I disagree; the system is up and running well before login. A rootkit, or backdoor from a Trojan, for example, (not that I'm saying this is what is happening) would have access to system resources before login.

Seems related to the wife's user account. Only happens after his wife has logged in. I think it is very unlikely to be a Permissons issue. And, if it is related to his or his wife's user, Permissions repair wouldn't even touch that.

Just a guess, but perhaps this is coming from a corrupted cache. Might try running Applejack.

Download:

http://sourceforge.net/projects/applejack/

Article on using:

http://reviews.cnet.com/8301-13727_7-10334620-263.html?tag=mfiredir

It runs in single user mode. After installing (you won't see it in the Applications Folder) hold CMD-S at startup. You will get a black screen with MS-DOS like text. Just follow the prompts: type in "applejack AUTO" and it will run through the following:

Correct any Disk problems.

Repair Permissions.

Clear out Cache Files.

Repair/check several plist files.

Dump the VM files for a fresh start.

Trash old Log files.

You can also run tasks selectively and for specific users by typing in "applejack." After running in "AUTO,"  you can go back and run it again as "applejack," steps 3 & 4 only, for your user.

The first reboot will take much longer than usual, as it rebuilds caches. It may take several restarts to see the benefits. Because of the deep cache cleaning in AUTO mode some applications may tell you they are being opened for the first time.

NOT YET UPDATED FOR LION

(Adapted from post by BDAqua)

Back on my 10.6. Might try moving this file, possibly corrupt, to the Trash (don't empty yet) located in the HD Library/Preferences. This is the middle library folder (not your Home Folder Library, not System Library) inside the main "Macintosh HD" Folder. You will be asked for your admin password for the move. This file should be recreated "clean" at next login, so log out and back in. If this doesn't help, just move it back from the Trash using File>Put Back.

/Library/Preferences/com.apple.loginwindow.plist

Did you find a solution to this issue?  I have the same issue since updating to El Capitan.

Your problem, hardware or software, may not be exactly the same as that of the original poster of this older thread, and it can be very confusing for everybody if we try to answer more than one question in each thread, which can also result in you applying the wrong advice to your particular problem.

In order for us to give your problem our proper attention to try to solve it, would you kindly start your own thread, describing the trouble you are having in the fullest detail, including completing your details to show what Mac or iDevice you are using, what operating system, and what version of the application in question. Please remember to post in the forum relevant to your hardware or version of OS X. A full list of all the support forums is here:

http://discussions.apple.com/index.jspa

I have the same issue with my iMac (OS X 10.11.1) 27" late '13. This issue has happened quite a bit lately, prior to and after software upgrade. I just want to clarify I'm having the same issue, so I can follow topic, hoping for solution. When coming out of sleep mode, when prompt for password box appears if you push anything (key) it's almost as if a key is stuck, auto types countless dots (discrete password dots), and repeatedly does it until you power off, and restart. ****(I've tried "switch user", "cancel"), but continues to do the same thing, as those are only options on that page.****

I had the same issue on a comparable age iMac.  Worked with AppleCare to diagnose, they determined it was the keyboard.  Replaced it (no charge with AppleCare) and the problem went away. 

Update:  Sadly the "autofill" at login continues, even after the new keyboard. Followed-up with AppleCare, they now think it is software related.  They had me use OS X Recovery ("command" "r" at start up) and reinstall the operating system.  So far so good, will post if autofill comes back.

I have the same problem.  Please post if you discover a fix.

I reinstalled OS X (see OS X: About OS X Recovery - Apple Support )  and the problem went away (so far).

Hope it works for you.

I had the problem first with my wire's login. Apple provided a new keyboard but the problem persisted. I removed her "login at wakeup" requirement and it seems to be fixed. Now, it's started doing it to me when I log in.

No help from Apple - seems they either don't know a fix or won't acknowledge the problem.

Apple doesn’t routinely monitor the discussions. These are mostly user to user discussions.

Send Apple feedback. They won't answer, but at least will know there is a problem. If enough people send feedback, it may get the problem solved sooner.

Feedback

I still have this problem. replaced the keyboard and the issue is still there