Symantec has updated its analysis of Stuxnet to include the new information on the intended target of the worm. The company said worm was looking for drives operating at very high frequencies 807 Hz to 1210 Hz relative to drives used for most industrial control systems. The worm targeted programmable logic controllers (PLCs) by Siemens Inc. and probably disabled machinery connected to them. The analysis lends credence to the theory that the worm was targeted at centrifuges used for uranium enrichment in Iran.
Source: https://threatpost.com/symantec-stuxnet-likely-targeted-uranium-enrichment-systems-111510/74672/