Experts from security vendor ESET warn that TDL4, one of the most sophisticated pieces of malware in the world, is being rewritten and improved for increased resilience to antivirus detection. ESET: Some components have been rewritten from scratch, while others remain the same as in previous versions. The new variants create a hidden partition at the end of the hard disk and set it as active. This ensures that malicious code stored on it, including a special boot loader, gets executed before the actual operating system.”]