Now I'll admit that my shadowrun history is a bit hazy, but I can swear this sounds familiar, inso much that wasn't there a story somewhere where folks use to share and swap bodies via the matrix? I recall a guy sharing taking over a woman's body for a night of fun and she woke up to her place a wreck with marshmellows and such.
Well, there's the Proteus board, which are basically metahuman biodrones for whoever the real master is behind the scenes, but other than that, the only way to go swapping bodies would be if two people were using rigged anthroform drones, or using magic, such as possession spirits or artifacts with crazy powers.
However, stories like what you are talking about do come up in Ghost in the Shell (where again, there are full-body cyborgs who sometimes switch bodies, but not via the matrix). The idea of something trying to take over and rewrite your consciousness via the computer has been done several times in cyberpunk and anime.