SoBig F, which caused chaos globally last week, is the sixth version of the worm.
Only SoBig A and F are still infecting PCs.
SoBig F will automatically stop infecting machines on 10 September. But a spokeswoman for Sophos said a new variant, which may also attempt to get infected machines to download code, is probably on the way after SoBig F self-destructs: ‘We are going to see a new version of the worm soon after.’
SoBig F contained instructions to try and download software from 20 sites between 2000 and 2300 GMT last Friday and again on Sunday.
Although the download windows on Friday and Sunday passed without incident, two more download windows will open this Friday and Sunday.
But Sophos said the worm was still clogging networks with the volume of traffic it creates. The antivirus company said that companies should install software that blocks executable code at the email gateway.
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