Fizzer is a self-propagating worm that spreads via e-mail and the peer-to-peer file-sharing service Kazaa.
On Friday, security company F-Secure gave Fizzer its second-highest alert status. On Monday, F-Secure issued a press release that upgraded Fizzer to its highest alert status, although it had not yet updated its Web site. Other security companies, such as Trend Micro and McAfee, have classified it as a "medium" risk.
The virus arrives in an e-mail with of a number of potential subject lines, including "So how are you?" "There is only one good, knowledge, and one evil, ignorance." "You must not show this to anyone." "Today is a good day to die." "Filth is a death." "Watchin' the game, having a bud." "Did you ever stop to think that viruses are good for the economy?"
Fizzer spreads in e-mail as an attachment with .exe, .pif, .scr and .com extensions.
When activated the worm sends itself to e-mail addresses stored in the infected PC's Windows and Outlook address books and drops into the Windows folder several files called initbak.dat, iservc.dll, iservc.exe and ProgOp.exe.
Messagelabs, an e-mail security company, said it intercepted almost 18,000 messages carrying the Fizzer worm on Monday alone, making it by far the most prolific virus currently in circulation. In comparison, there were about 6,000 interceptions of Klez, which has topped the virus charts for the past 15 months.
More than 40 percent of all Fizzer interceptions were in China, according to MessageLabs.Silicon.com's Will Sturgeon reported from London.