You have chosen to open st
which is a: application/octet-stream
from: http://ad.yieldmanager.com

What should Firefox do with this file?

Open with…
Save File…

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Well, you get it, that’s my problem, its asking me to download this stupid spyware all the time. Please tell me how to block it in Firefox, do not tell me to download additional software because i won’t. I have Spybot and Avast, i scanned my PC, immunized it, deleted all unknown files, deleted all temporary files in safe mode and scanned my system several times. No way to get rid of this stuff. Please help, i am really desperate.
@Wooly

Yes, i allready did that, and i scanned my computer with several antivirus programs: Avast, Norton, Kaspersky, Avira.

No result.
I forgot to mention: It only happens when i am on a Yahoo site. I think someone is targetting my IP connection.