Antivirus Add-On for IE to cause 5 times slower page load times

The dynaTrace AJAX Community has been really active lately – with lots of great forum posts and “discoveries”. As the Community Lead I want to update you about the recent activities as there are several topics that should be interesting for everybody that is interested in Web Performance:

Antivirus Software to cause page load times to slow by 5x

In the last two weeks I had a conversation with two of our AJAX Edition users (Pedro and Frank) who ran into the problem they posted on our Dynatrace AJAX Forum.

The phenomenon was that when Dynatrace AJAX was enabled, page load time was about 5 times faster than without Dynatrace. Sounds almost like the perfect sales pitch – right 🙂

We exchanged sample HTML files in order for me to reproduce the problem to identify what Dynatrace does underneath the covers that speeds up web performance. I couldn’t reproduce it which led us to the conclusion that there must be something else on their machines that slowed down the page load time when Dynatrace is not enabled. Last week Pedro and Frank came back to me as they figured out what the problem was. In his final comment Pedro says “We have finally found the source of the problem. The McAfee corporate antivirus was checking the scripts and hence slowing down the rendering of the page, and it seems that Dynatrace somehow disabled the antivirus making load times much faster. Thanks Andreas for your support. Pedro.

So it seems that the Antivirus Add-On in Internet Explorer is causing a major impact in page load time. The AV Add-On needs to check all loaded JavaScript files for malicious code. In the example of Pedro and Frank they load jQuery, several jQuery plugins and some custom JS. This slows down their page load time as the browser cannot continue downloading additional content until the JavaScript files have been fully downloaded and executed.

Why is it faster with Dynatrace enabled?

dynaTrace hooks certain APIs from Internet Explorer and the underlying Network APIs in order to capture network round-trips and instrument JavaScript code. We once ran into the problem that the Real Player Plugin impacted our ability to capture Network Traffic. We assume it is a similar problem that happened with the Antivirus Add-On. Dynatrace uses the Network API’s to capture Network Traffic and prohibits the AV Add-On to capture and analyze the downloaded JavaScript files as well.

What does this mean for you?

First of all it means that you want to test your web sites with and without any type of plugins your users may have – Anti Virus Plugins are a good example as we have learned that they can dramatically impact web page load times. It also means that certain Antivirus Plugins can easily be disabled by another plugin – which defeats the purpose of an Antivirus Plugin. Make sure to test the combination of Add-Ons and whether they impact each other.

Skype Plugin to also slow down page load time

A similar problem was previously reported and I blogged about it in How to identify IE Add-Ons such as Skype that impact Web Site Performance.

Thanks for being active in the Dynatrace Community. Keep the posts coming!

Andreas Grabner has 20+ years of experience as a software developer, tester and architect and is an advocate for high-performing cloud scale applications. He is a regular contributor to the DevOps community, a frequent speaker at technology conferences and regularly publishes articles on You can follow him on Twitter: @grabnerandi