Due to the extreme level of personal information stored on a grain there is obviously a very high risk of security concerns. While The Entire History of You never mentions networked communication, it does discus the inherent risks that any physical technology has. The first mention of these risks is at a dinner party where a character mentions that her grain was physically gauged out of her neck when she was mugged. While it is implied that many people encrypt their grains, whoever stole hers had full access to every moment of her life. It is unclear why her grain was not encrypted, but after she lost it she decided she preferred not having one. The characters assume that her grain was sold for the footage of her sexual encounters.
No security system is ever good enough to stop someone who is able to threaten someone with access to the data, and there are multiple examples of this in the episode. When Liam is drunk he threatens Jonas with a broken glass bottle to delete all footage of Liam’s wife Ffion from his grain. Later, after Jonas’s footage revealed he was still having an afair with Ffion, Liam forces Ffion to show him what happened. While she claims to have deleted the footage from their encounter, this defense fails because of the lack of a gap in her continuously recorded timeline.
Additionally, there are refernces to remote backup systems for the grain, which could introduce large security risks. An advertisement for a grain upgrade references decades of free backups which introduces several obvious risks. Any vulnerabilty in the backup system, or insider with secure access could potentially have access practically all personal data anyone knows about themselves.