unveiled new tracking technology that makes use of different kinds of cookies to address the issue of cookies overwritten during the sales process, effectively removing the commission opportunity for the affiliate that generated the click.
You can read the whole article here: unveils new technology to protect certain affiliate transactions

An excerpt from the release:

Hard Click
When a site visitor clicks on an affiliate link, a standard tracking cookie is set on their computer. If the visitor clicks on multiple affiliate links for the same advertiser, the last click overwrites the first cookie and receives the commission payment.

Soft Click
When a site visitor solely interacts with a link provided by a soft click cookie partner, the affiliate is awarded the commission payout in the normal way. If an affiliate cookie is already present prior to a customer’s interaction with the soft click affiliate, the original site with the hard click cookie receives the commission payment.

If no hard click cookies are present, and more than one soft click cookie affiliate is involved in the conversion process, the last click model applies.