in my asp.net application I'm calling a site, which is producing a .pdf file of the content of the viewed page.

In IE 9 everything is fine - the browser opens a new window and there the pdf file which has been created can be opened or saved.

In IE 7 and 8 the window opens, but after a second the window closes automatically and the result is, that the pdf file cannot be viewed.

*This occurs only in secure internet (with `https`), not intranet.*

If I add my site to "trusted sites" in the IE properties, then everything works fine.
Can i manage this problem with some code?
(I cannot simply tell my users to add the page to trusted sites)