Throughout the system, in both the old and new economies, mooching is one of the most frightening crimes that can occur. Moochers are parasites, implanting themselves into people's lives for as long as possible to and feeding on their resources, and most terrible of all is you can't ever be sure when its happening.
There are two methods. By far the most common is to take the place of someone who actually exists, usually a reasonably distant relative. The usual method is to create a predictive profile, use that as the basis for psychosurgery turning yourself into a reasonable imitator, and either discretely assassinate them or arrange for them to be out of contact, then step into their place.
The much more difficult method is to create a relation out of whole cloth. This requires creating a fake identity and supporting evidence such as social networking, and psychosurgically implanting the appropriate memories into the target and usually many others. Creation of an identity capable of fooling someone while maintaining a false relationship is a very difficult piece of forgery. No public proof exists of this having ever been done, but rumors abound that such and such person is completely fake, created by Anarchist/Consortium/Jovian agents.
The extent to which these crimes actually exist is debatable. Their very nature means it is difficult to determine when one is occurring, and often when one has occurred. There have been only eleven proven cases, none of which lasted longer than two weeks. The social networked, sousveillance societies of modern transhumanity make it a virtually impossible crime in most places.
Plot Hook: One of the PCs has an old friend. At least, they have memories of them being a friend, videos, photographs, chat logs and mutual friends, but what does that prove, really?