The MyDoom.A worm is already being touted as the most prevalent internet virus of all time, as its global rampage yesterday quickly rose to infect one in every nine of all internet emails.

Security firm Central Command warned that corporations and home users were being bombarded with infected messages.

Steven Sundermeier, vice president of products and services at Central Command, said: "The extremely aggressive nature of this new worm, which is less than 24 hours old, has demonstrated that the global email infrastructure is still very vulnerable to such attacks."

The firm warned that the virus could create a "global army" of infected PCs that the virus writer could control.

MyDoom carries multiple malicious payloads, including the ability to turn infected machines into transparent proxies to launch other kinds of attacks.

The infection makes compromised PCs wait for commands from the virus author on TCP/IP port 3127.

Experts are still trying to establish the full implications of the distributed denial of service (DDoS) attack built into the worm, which will launch a sustained attack against The SCO Group's website from 1 February till 12 February.

SCO has offered a $250,000 reward for information leading to the arrest and conviction of the author of the virus.

Darl McBride, president and chief executive of SCO, said: "The perpetrator of this virus is attacking SCO, but hurting many others at the same time.

"We do not know the origins or reasons for this attack, although we have our suspicions. This is criminal activity and it must be stopped."

The virus is not the first to attempt to launch attacks against a corporate website, but looks like being the largest threat to date.

Last year Microsoft saw off an attempt to launch a DDoS attack against its website by the writers of the Blaster worm with minimal disruption.