Flame is much bigger than both Duqu and Stuxnet, which at around 500KB in size were already considered large by security experts. The size of all Flame components combined adds up to over 20MB and one file in particular measures over 6MB alone, Kamluk said.

Another interesting aspect of the threat is that some parts of Flame were written in LUA, a programming language that's highly uncommon for malware development. LUA is often used in the computer gaming industry, but Kaspersky Lab hasn't seen any malware samples before Flame that were written in the language, Kamluk said.

Flame spreads to other computers by copying itself to portable USB devices and also by exploiting a now-patched Microsoft Windows printer vulnerability that was also leveraged by Stuxnet.

The Kaspersky researchers haven't found any evidence of an unknown (0-day) vulnerability being exploited by this malware, but Flame is known to have infected a fully patched Windows 7 computer, so they don't completely exclude the possibility, Kamluk said.