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I have two laptops, one of them has no problems whatsoever when it comes to browsing the internet, everything is speedy and pages load as expected.

The other one however, is a nightmare. Pages load slow, and it looks like the browser just sits there and waits a bit before it starts to load pages.

So I installed Fiddler to check the requests that are happening and how long they take to complete.

However, once I start capturing using Fiddler, the browser becomes speedy, and the pages load more or less as on the first laptop.

  • So once Fiddler starts, browser speed is normal
  • I experience this behavior in all major browsers (chrome, IE, and firefox)
  • I have checked the internet options, and there are no proxies configured

Can anyone explain me what is going on?

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Have you verified the laptop in question is virus/malware/spyware free? – CharlieRB Dec 27 '12 at 20:26
Have you tried visiting pages never visited before to make sure your not getting a cached version? Try running speed test with and without fiddler running, and try it on the other laptop too. – Celeritas Dec 27 '12 at 20:38
@CharlieRB yes, I ran several virus scans and no issues were detected. also I cannot find anything suspicious in the running processes or services. – thomasvm Jan 2 '13 at 13:23
@Celeritas the Speed test reveals that the speed is in the same order of magnitude as on the fast pc. – thomasvm Jan 2 '13 at 13:24
Fiddler caches DNS responses, but so do browsers. When you say "no proxies are configured": What exactly are the settings inside IE's Tools > Internet Options > Connections > LAN Settings? – EricLaw Jan 14 '13 at 22:31

I think it's a virus that "hooks" queries of your http port.
If Fiddler uses the same hooking method, it can stop hooks of another "hookers" (in this case - virus).

Thoroughly check your OS for viruses using powerful antiviruses such as Kaspersky IS or Norton IS.
Use Sysinternals' Autoruns.exe to check ALL autoruns (because MSConfig doesn't show ALL autoruns). Also use ProcMon.exe to see which programs are running and which are using internet when you're connected to the net. These tools will help you to catch virus.

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This could be because of some hardware problem, maybe in case of the internet adapter of your laptop.

If nothing else solves and if you are willing to spend some money, you can have it replaced with a new one.

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