Spabot.AS is a Trojan that modifies the LSP layers (Layered Service Provider) in order to filter the traffic generated.
Additionally, it sends massively spam. The email messages it sends contain information about a certain medication and a link to a certain website.
Spabot.AS 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.
LSP (Layered Service Provider) is a Windows feature that is used to listen to all the TCP/IP traffic taking place between Internet and the applications that are accessing Internet (such as the web browser, the email client, etc.).
Within this structure, a number of programs are specified. Such programs will carry out certain actions over the TCP/IP traffic; for example, it could be specified a computer security program, which analyses the traffic in search for viruses or other threats before transferring it to the final application of the traffic.
However, this structure can also be used by certain malware, in order to intercept the communication across the Internet, and, what is worse, if they are deleted without taking precautions, the Internet connection will stop working indefinitely.