BBC News reports security researchers estimate 4.5 million PCs have fallen victim to the TLD-4 virus over the last three months. The TLD-4 botnet is deemed the most sophisticated threat today, it's well protected against attacks, competitors and anti-virus companies. The virus hides in Windows's master boot record, uses a custom encryption system to protect communication between those controlling the botnet and sends out instructions via a public peer-to-peer network rather than centralised command systems.
The 4.5 million PCs have become victims over the last three months following the appearance of the fourth version of the TDL virus.
The changes introduced in TDL-4 made it the "most sophisticated threat today," wrote Kaspersky Labs security researchers Sergey Golovanov and Igor Soumenkov in a detailed analysis of the virus.
"The owners of TDL are essentially trying to create an 'indestructible' botnet that is protected against attacks, competitors, and anti-virus companies," wrote the researchers.