How to stop this attack on my computer!?

[DunbarPappy®ϟϟ]

How you got nailed:
His account may have been compromised, and sent you a weaponized mail, with a link to a malicious server.
These tricks (common across many social network sites) send a provocative message which entices the recipient to follow a link. While there a splash screen with an "Update your flash player here" button.
It may look official as hell, but it's the unseen "iFrame" that holds the real URL which you will be taken to.
Since almost everyone has gotten use to the constant updating of Flash, they go ahead and click the "install' button and the deed is done.

You must never click a link offered on a site. Always get Adobe products updated right from the official Adobe site using the normal channels.
It's hard to say what's been installed, but seriously, it could be anything in the world.
Since it's trying to reach back to the 'Net, it likely is a "Trojan downloader", getting more rubbish to install.

Good luck.