Internet security experts have described the TDL-4 botnet as ‘indestructible,’ claiming it is not an easy nut to crack.

Sergey Golovanov and Igor Soumenkov, security researchers from Kaspersky Labs, warned that changes introduced in the fourth version of the botnet, TDL-4, made it the most sophisticated threat to computers.

Speaking on the topic, one of the software security experts said, "TDSS uses a range of methods to evade signature, heuristic, and proactive detection, and uses encryption to facilitate communication between its bots and the botnet command and control center.”

In addition the botnet is equipped with a powerful rootkit component that lets it mask the presence of any other sort of malware in the machine.

According to estimates, TDL has so far infected as many as 4.5 million computers around the globe following the appearance of the first version of the botnet.

The botnet, which affects Windows PCs, infects the victim’s machine and gain remote control of it. It pilfers the victim’s confidential data from the machine and uses the machine to carry out other attacks and send out spam.

Twenty-eight per cent of TDL’s victims are from the US, while India and the UK are thought to have around 7 and 5 per cent of affected machines, respectively.