The spread of the virus is slowing down, compared to the 320,000 infected e-mails spotted by anti-virus firm MessageLabs last week, but is still on track to be the most prolific e-mail virus to date.
"I would say it's rampant," said Technical Director for MessageLabs Angela Hauge.
It has been picking up in the United States. On Monday Bugbear infected PCs sent out nearly 38,000 e-mails worldwide.
Difficult to find
After it infects a PC, the Bugbear virus searches the machine for e-mail addresses and sends a message out to each address, with a copy of itself attached.
It can disguise itself as a random e-mail, making it difficult to spot and to trace back.
Bugbear takes advantage of a known flaw in Microsoft Outlook to replicate itself without the need to click on the attachment.
It can also disable anti-virus protection, as well as compromising passwords and secure transactions and leaving an open door in computers for hackers.
A bug within the virus means that it can sometimes cause printers to start printing out nearly blank pages.
Senior Anti-virus Technologist with MessageLabs Alex Shipp said that, because it exhibits few symptoms on an infected computer, users may not know that their systems are infected.
He urged users to make sure that their anti-virus software was upgraded regularly.
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