Dialer.GUW is a dialer type malware. Dialers usually try to establish phone connections with high rate numbers, significantly increasing the phone bill of the affected user.
Dialer.GUW affects computers that use a modem to connect to the Internet, as the virus modifies the Dial-up network access settings. It changes the telephone number provided by the ISP (Internet Service Provider), which is a local-rate number, to a high-rate number.
It reduces the security level of the computer:
it opens one or more ports to allow remote access to the computer and takes action that compromises user confidentiality.
Dialer.GUW does not spread automatically using its own means. It needs an attacking user's intervention in order to reach the affected computer. The means of transmission used include, among others, floppy disks, CD-ROMs, email messages with attached files, Internet downloads, FTP, IRC channels, peer-to-peer (P2P) file sharing networks, etc.