How to insert alert window in the http body

[willieh811]

Greetings,

I have an application were I need to intercept a file download, detect a virus, and alert the user that the downloaded file has a virus. I have to add this as I monitor the page that the user is dowloading the file from. I am trying to figure out if it is possible to insert the alert as if it were part of the page the user is viewing so that the alert window shows up after the download.

Is this possible?

[TheBearMay]

....
document.getElementById("alrtMsg").innerHTML="<h1>Virus Detected</h1>";
....
<div id="alrtMsg"></div>
...