Tenga.A is a virus with worm characteristics that downloads and runs the Trojan detected as Downloader.DNX.
Tenga.A shows a very a complex infection routine, which it uses in order to infect all the executable files on the computer, excepting NTOSKRNL.EXE. It is even capable of infecting files belonging to the operating system, as it disables the characteristic known as Windows File Protection.
Tenga.A spreads by attacking IP addresses, in which it tries to exploit the vulnerability RPC DCOM.
Additionally, as Tenga.A infects files, it could also reach computers when the infected files are distributed through any of the typical means of tranmission, which include, among others, floppy disks, email messages with attached files, Internet downloads, FTP, IRC channels, peer-to-peer file sharing programs (P2P), etc.
If you have a Windows 2003/XP/2000/NT computer, it is very recommendable to download and install the security patch for the RPC DCOM vulnerability.