Lasco is a worm for Symbian OS that uses Bluetooth to distribute itself to other Bluetooth devices in "Discoverable Mode". Users generally receive Lasco as Velasco.sis and if installed, Lasco will begin searching for nearby Bluetooth Enabled devices to send itself to.  In addition to replicating in this manner, Lasco can also embed itself into other .SIS files on the infected device.  Thus if these .SIS files are transferred to another device and installed, the user will also be prompted to install Velasco.sis.