A freely available peer-to-peer (P2P) hacking tool has become the weapon of choice for many hackers looking to take control of users' PCs.
The P2P hacking software - known as Phatbot - was identified by the US Department of Homeland Security earlier this month, causing officials to email warnings to a number of IT security software vendors.
Using modified viruses, hackers are reported to be launching distributed denial of service (DDOS) attacks by quietly taking background control of other users' PCs across the Internet.
Because the bandwidth usage is minimal, and the passive malware sits in the background on the users' PC, only springing into life when called by the hacker, it is said to be difficult to spot using many commercial IT security packages.
Unconfirmed reports suggest that the vendors are planning to update their software to help protect against the Phatbot problem.
Phatbot has been described as a Swiss Army knife of attack and snooping software, taking a polymorphic approach to its installation on the host PC, to avoid conventional AV scanning applications.