Antivirus companies have warned customers about a new e-mail virus that is spreading on the Internet.
W32.Mimail is a mass mailing e-mail worm the arrives in email in-boxes disguised as an administrative email sent from an organisation's own administrator.
Messages use the subject "Your Account" and contain the virus in an executable attachment called "message.zip".
When released, the Mimail virus captures email addresses from a user's hard drive and sends copies of itself out to recipients using a built-in SMTP (Simple Mail Transfer Protocol) engine, according to F-Secure.
Companies including Symantec, Network Associates, and F-Secure have issued warnings about Mimail.
Most companies rated the new worm a "medium" level threat, indicating that the worm was infecting customer sites and spreading.
Despite the warnings it is still not clear how quickly, or even whether, Mimail is spreading, according to Vincent Gullotto, senior director at Network Associates' McAfee AVERT Labs.
"The initial numbers look like people are getting hit pretty hard - maybe even a high alert," Gullotto said.
However, the large number of reports about Mimail may just be evidence of a spam-like initial distribution, or "seeding" of the virus, he said.
That would make Mimail similar to another recent email containing a malicious program, Downloader-DI, he said.
That virus set up a secret back door on infected machines and downloaded instructions from a hacker Web site.
After flooding email in-boxes in an initial spam distribution, however, Downloader-DI died out when other users failed to open the attachment that installed the Trojan program and replicated the message, Gullotto said.
However, the Mimail's spread could also be due to its ability to mask itself as an internal administrative message, tricking users into trusting the message, he said.
In addition, Mimail's malicious code was embedded in a compressed format file, making it difficult for some gateway antivirus products to detect the attack, he said.
While it appeared Mimail simply steals email addresses and sends copies of itself out to unsuspecting users, McAfee AVERT was still studying the virus for other malicious activities such as installing Trojan programs that could allow malicious hackers to gain access to the machine at a later date, Gullotto said.
Antivirus companies, including Network Associates' McAfee antivirus unit, have posted updated virus identity files for Mimail and encouraged users to update their antivirus software.