The latest version of the SDBot worm opens a back door for hackers and then relays stolen information via a network sniffer and keystroke logger embedded in the code.
The worm has the potential to intercept passwords and PayPal account details on networked computers.
Network sniffers monitor network traffic. Hackers use them on compromised PCs to intercept data packets, such as login details, which allow them to access to other computers.
The SDBot advisory came from antivirus firm Trend Micro.
"The complete SDBot family is dangerous, but it's not spreading that fast so our risk rating is low," said Raymund Genes, European president of Trend Micro. "The SDBot is perfect for spying, but anyone with updated antivirus protection should be fine."