I wanted to share this experience with all. I eventually fixed it, as explained in below own-answer.

Lately, I noticed that some operations on my Windows 7 box were becoming slower and slower as days go by. I specifically faced this:

  • after having started a Java Web Start application (JWS): clicking some part of the GUI led to a delay before having the expected result.
  • after having started an application from a remote Linux box, using X11 forwarding, thanks to an X server for Windows: as with JWS, actions were delayed. BTW, I faced it with different X servers for Windows, so the X server itself didn't seem to be in cause.
  • upon launching an elevated operation: e.g. starting any application as Administrator. In that case, I faced a delay when the UAC window was displayed, with the message "Looking for credential tiles" lasting for a while.

In all above cases, I faced no actual delay just after having rebooted Windows, then the delay was increasing as days were going by. After 3 or 4 days, JWS or X11 forwarded apps were simply no longer usable due to delays above the minute. Similarly, after a few days, starting an elevated operation needed to wait for several minutes with the message ""Looking for credential tiles" until local Administrator account was proposed!

I investigated repeatedly to figure out what was causing such behaviors, knowing that it started once in the recent past (i.e. I wasn't facing this before):

  • First, I thought about some malware: but my installed AV, Avast Free Antivirus, didn't find anything.
  • Then I inventoried running services, stopped some, based on "personal suspicion" or based on what they were expecting to do. But no luck either.
  • Did the same with installed apps: even uninstalled most of them. Still no luck.

So, I had to work with this "pain" for quite a while, rebooting when it was becoming too unbearable.

I finally pinpointed the culprit: Avast Free Antivirus! Indeed, after fully disabling it, I no longer experienced any delay.

Before deciding to switch to another AV, I chose to determine if that was due to some specific option that I would have enabled a while ago and that induced the increasing delay issue. The other possibility was that an avast update introduced some bug that led to this.

And I figured out that it was due to "Settings-Troubleshooting-Enable anti-rootkit monitor" option: once disabled, I no longer faced any delay for the 2 first cases.
But, unfortunately, this doesn't solve the third case (UAC), contrary to what I once thought. This one has another source that I still have to discover...

BTW, to test, I used to start xeyeson a remote Linux box:

  • with above option enabled, the eyes were displayed after a few seconds,
  • when disabled: the eyes were immediately displayed, without any delay.

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