Infections as a result of the infamous Conficker (Downadup) worm have peaked at around the 10m PC mark.
Variants of Conficker use a variety of methods to spread, including exploiting the MS08-067 vulnerability in the Microsoft Windows server service patched by Redmond in October. Once it gets a foothold within corporate networks, Conficker is programmed to spread across local area networks. The worm also spreads between infected USB sticks and Windows PCs.
Compromised Windows PCs are turned into drones in a botnet, programmed to phone home through a changing series of servers. It's this latter behaviour that has allowed F-secure to track the progress of the worm over the last two weeks or so. Its latest educated guess of the size of the botnet is 10m strong as of Friday, 23 January, 1m up on the 9 million of the week before.
The 9m on 16 January compares to 2.4m on 13 January, so the growth rate of the botnet is clearly flagging.
That still leaves the huge problem of cleaning up infected systems, preferably before they are abused to send spam or other malfeasance. The Conficker botnet remains dormant at the time of writing. F-secure stresses that its latest estimate is at best an educated guess, because of a number of factors that make estimating the size of the botnet problematic.
As time passes, the number of estimated Downadup infections becomes more problematic to calculate as we are monitoring a varying number of domains. Re-infections may also be inflating the count. In any case, today seems better than the day before and we think that the growth of Downadup has been curbed. Disinfection of the worm remains a challenge.
Some countries are being more heavily hit by the zombie epidemic. China, Russia and Brazil account for 41 per cent of infected IP addresses, F-secure reports. By comparison, only one in 100 infections stems from an infected machine in the United States.
Conficker represents a return to the network worms of yesteryear, infections such as Nimda, Sasser and Blaster. Reasons for the return of the problem after years of dormancy have been unclear - the best we could dig up when researching the issue last week that writing network worms was too much like hard work.
F-Secure security adviser Sean Sullivan has a more sophisticated theory that seems to ring true.
"We haven't seen a worm like this in several years because Microsoft learned from the past, and Microsoft Updates does a good job," Sullivan told El Reg. XP Service Pack 2 turned on the Windows Firewall by default.
"Also the production of malware moved from hobbyist to professional; worms create too much noise typically." ®