Recent reports from NetWitness, a site which tracks infections, suggest that a new infection called the Kneber botnet has infected over 75,000 systems as of this posting date. You can read more about these reports in this article from Reuters.
A botnet is like a virus which takes control of a system and executes certain commands or programs. The infected systems becomes a robot.. or bot for short.. doing the bidding of the hacker who controls the botnet program. Previous botnets have compromised everything from NASA to the power grid.. but to date have been mostly used for attacks (called denial of service attacks) on public websites by making all the bot computers attack the website at once, overloading it. This new botnet appears to be geared strictly for obtaining information like logins, passwords, account numbers, and access codes. Given the complexity of this botnet, it is most likely something created by an advanced group of hackers.. or possibly a foreign-sponsored government.
As with all viri, spyware, and malware, the best way to protect yourself is to follow safe computing practices. These include not opening attachments you are not expecting, not visiting websites that use pop-ups, and keeping your system up-to-date with anti-virus and anti-spyware software. Even with normal precautions, a botnet like Kneber can still infect your system by jumping from a nearby system or server. ESG recommends running a full anti-virus scan at least once a month (ideally schedule one to run automatically one a week) to find any deep infections like this.