False Positive in Internet Explorer

My customer who use avast complain about malfunction of Internet Explorer.

Symptom

Cause

  • When download XML file using XMLHTTP, Avast inject HTML5 Doctype incorrectly and it cause exception.

  • below is snippet of original XML file

<?xml version="1.0" encoding="UTF-8"?> <?xml-stylesheet href="/DAELIM/common/css/Daelim_all.css" type="text/css"?>
  • below is snippet of XML file that modified by avast
<?xml version="1.0" encoding="UTF-8"?> <?xml-stylesheet href="/DAELIM/common/css/Daelim_all.css" type="text/css"?>

In the XML Specification, xml declaration allowed only at the start of the document.
So if you need to inject DOCTYPE, you must inject DOCTYPE after XML declaration.

This doesn’t seem to be a problem with avast.
The same problem appears also when all avast shields are disabled.

With all shields enabled, the problem appears only in IE.
Not in Opera, FireFox, Chrome and Maxthon

Thank you for your reply.

I know. The same problem appears also even all avast shields are disabled.
But when I uninstall avast, everything is OK.

Avast installs InternetExplorer addon, I think that causes the problem.

What exact IE version?
What exact avast version?
What exact OS/SP?

Could be it is specific to a certain version.
Let’s test it.

OS : Windows 7 Ultimate K (using Korean Language)
SP : Service Pack 1
Browser : Internet Explorer 10 (10.0.9200.6844)
Avast : Latest Version (filename : avast_free_antivirus_setup.exe, download: 2014-04-01)