NETWORK ACTIVITY VALIDATION

Methods, systems, and apparatus, including computer programs encoded on computer storage media, for validating network activity. One of the methods includes receiving data identifying network activity for an online account; determining one or more users associated with the online account; determining, for each of the one or more users, a current physical activity in which the user is participating; determining, for each of the current physical activities, a likelihood that the corresponding user initiated the network activity while participating in the current physical activity; determining, for each of the current physical activities, whether the corresponding likelihood satisfies a threshold likelihood; and in response to determining that at least one of the corresponding likelihoods satisfies the threshold likelihood, providing an alert about the network activity to one of the one or more users associated with the online account.