JOHANNESBURG, July 23 (Reuters) - South Africa"s state-owned firm Transnet said on Friday it had identified and isolated the source of disruption to its IT systems that impacted its container terminals. The freight logistics firm was hit by a suspected cyber attack, three sources with direct knowledge of the matter told Reuters on Thursday. read more Transnet, which operates major ports and a huge railway network, said it was prioritising the export of reefer containers, used mainly to transport perishable cargo at a controlled temperature, primarily through the port of Durban as this was the peak of the citrus season. Miner Barrick Gold (ABX.TO) said on Friday that it did not ship through Durban and that it was unaffected.