Sophos has today warned that the mass-mailing W32/Sobig-F worm, which
has flooded computer users this week, could attempt to download a
Trojan horse between 8pm and 11pm BST today.
At 19:00-22:00 GMT (which is 8-11pm in the UK) on Fridays and
Sundays, the worm has been programmed to automatically direct
infected PCs to a server controlled by the virus writer from which
a malicious program could be downloaded. At the moment, it is not
known what the download material will do, but possibilities include
launching another virus or spam attack, collecting sensitive
information, a denial of service attack, or deleting files stored
on an infected computer or network.
"The main effect of Sobig-F to date has been to slow down the
internet with the sheer quantity of emails it has generated," said
Graham Cluley, senior technology consultant at Sophos Anti-Virus.
"At 8pm tonight, most British companies will have left the office
for the bank holiday weekend, but any infected computers that are
left on have the potential to become zombies, doing whatever the
virus writer wants. If the writer of Sobig succeeds in installing a
Trojan on infected PCs, users could be in for a nasty shock when
they return to work next week. The message is simple: ensure your
anti-virus is up-to-date, run your anti-virus to check for
infection, disinfect if necessary and ensure your computer's
firewall is properly configured."
"What the worm downloads will not be known until this evening -
it could display an offensive but largely harmless message or
launch a malicious attack. But the download is timed to coincide
with the regular business afternoon in the United States, so users
should be concerned about unauthorised code running on their
computers. On Monday morning businesses in the Far East and
Australia will be beginning their working day when the worm tries a
second time to download unknown code from the net," continued
Sophos advises that the download can be avoided by configuring
firewalls to block outgoing connection attempts to UDP port 8998.
In addition, anti-virus software should be updated, and any
infected PCs disinfected.
Sophos has published information about how to
disinfect computers and prevent the Trojan download.
Sophos is headquartered in Boston, US and Oxford, UK. More information is available at www.sophos.com.