However, in certain countries (for instance, India and Mexico), the patent on Sildenafil citrate has expired - meaning that it can be manufactured in these countries very cheaply indeed. Pharmacy websites have sprung up to act as a channel for distribution, likely operating outside of the USA, and charging in the region of $2 per pill - and at nearly a fifth of the cost to the US consumer, this mode of distribution is a very popular way to .

With this profit comes great competition, however, so off-shore pharmacy sites have resorted to one of the most popular forms of product marketing on the internet - affiliation. With massive profit margins to fall back on, pharmacy companies can easily offer commission rates of around 40% to their affiliates - a very tempting offer to some people. Affiliation of this nature is ideally suited to spam - the affiliates are legally separate from the online pharmacy, so the pharmacy itself is in no way liable for the illegal bulk email - the onus there falls to the mysterious spammer, likely hid behind false identities and proxy servers. Obviously, for the pharmacy this is ideal - and it provides an ideal opportunity for spammers to make a quick profit.

Click rates for email campaigns are difficult to know exactly - it largely depends on the campaign, the success in evading email filters, and the format of the email itself. However, generally speaking it is very low - reports suggest a typical figure of around 0.02%. Supposing the spammer sends 1 million emails in a day - not an unlikely figure given the ease of sending email - this means the spammer can expect to see 200 clicks through to the online pharmacy store. Conversion rates are likely to be much higher - I would expect 1% to be a typical figure, but again, this can vary between campaigns. At this figure, then, the spammer can expect to see a handful of orders per million emails. Typical order values are quite high though - price breaks help push the lowest viable purchase to at least $100. If we assume $100 as the average transaction, 40% commission means the spammer will net $80 per million emails sent - all considered, not a bad return.

Of course, there are running costs involved - DSL lines, computers, email lists - but assuming the spammer can send a million emails a day, he/she will earn $29,200 per year - not a bad sum, considering the minimal work involved. And if you scale up the figures - say the spammer has the capacity to send 5 million emails a day, and the capability to attain the same sort of conversion ratio, then the potential yearly earnings are $146,000 - an impressive amount by any standards.