An ICT systems error which halted trading on the Australian Stock Exchange (ASX) on Monday afternoon has been traced back to a software problem. After investigation by technical staff, it was found the exchange’s computer system was not sending trading confirmation messages to some companies listed on the ASX. “The issue created a duplication of internal series identification numbers which impacted a component of the trade system,” an ASX spokesperson said in a statement. “All impacted trade executions remain valid and all post trade processes were completed as per normal.” The messaging problem affected one fifth of the market. For operational purposes, the ASX market is split into five segments. ASX staff planned to look at a permanent resolution to the software issue. Trading was expected to resume today at 10am (AEDT). ASX Trade uses Nasdaq OMX Group's Genium INET platform which was implemented in November 2010 to improve latency and boost the number of orders processed. It replaced an older Integrated Trading System (ITS) that had been used by the ASX since October 2006. The spokesman said this was the first time the trading system had gone down. "What happened yesterday with the halt to the market was a very rare event. We don't know yet if the software will be replaced, that's to be determined," he said.