Aside from pre-selling your products and affiliated offers, the other purpose of your free viral report should be to build your mailing list.
This is because if you are unable to pre-sell, let alone sell, the products and services featured in your free report, the last ditch effort should be to collect leads. In short, if you cannot convert the reader into a ready buyer, you should then attempt to convert him or her into your subscriber.
In that manner, you can still follow up with your reader on future offers and have a chance at converting him or her into your customer, preferably lifetime.
You can do so by offering a lifetime update to your report or a unique notification list your reader will be interested in subscribing to, which leads to having him or her subscribed to your mailing list.
One of the few success factors in viral marketing of your free report is quality. If your readers find your information worth sharing, and you encourage them to do so by giving them the right to give your report away for free, you will be able to have your name, status and links within the report passed around without any effort on your part - simply because others are willing to do so for you!