Geo-location services allow users to share their location with friends on social networks. These services provide value to businesses by allowing them to see which customers are most loyal and reward them. Check-ins through these services can have a viral effect by increasing a brand's visibility through a user's social networks. Popular geo-location services mentioned include Foursquare, Loopt, and Gowalla. While these services provide benefits, they also raise privacy and safety issues regarding how user habits and locations are tracked.