A bungle by Australia's biggest bank, which led to the largest ever corporate fine in Australia, will be front and centre in the High Court in Canberra today, as a group of shareholders pursue the bank for damages over inflated share prices.The Commonwealth Bank paid $700 million after it was fined by financial intelligence agency AUSTRAC for breaching anti-money laundering and terror financing laws.AUSTRAC went after the bank over systemic failures, which included the late filing of 53,506 transactions of $10,000 or more through its "intelligent deposit machines" between 2012 and 2015.That breached the law, which required banks to report transactions of that amount and above within 10 business days so AUSTRAC could check whether the money was going to gangs or terrorist networks.The breaches also included failing to properly monitor 778,370 accounts to check for money laundering red flags and not checking suspicious customers.The bank settled the case and agreed to pay the massive fine in 2018.But the fact of the breaches had not come to light until a media release from AUSTRAC in 2017, despite being known earlier.Today, the shareholders will tell the High Court the bank failed to make the situation public when it realised there was a problem and they are entitled to compensation "for the inflated value of their shares attributable to the bank's wrongful failure to inform the market". The submissions to the High Court said that failure saw "CBA shares traded on the ASX at a higher price than that which a properly informed market would have set; and that group members acquired CBA shares in that inflated market and, consequently, paid too much for them."The share price dropped by $3.25 at the announcement."The loss for which they sought recovery was the difference between the inflated price and the price they would have paid for their shares had the market been been informed," the shareholder submissions said.Failed bid to quantify lossesThe Commonwealth Bank previously apologised and said it had spent $400 million to fix the problems. (ABC News: Keana Naughton)A bid to establish damages failed in the Federal Court, which found the shareholders could not "quantify" the losses.The group wants the High Court to find the lower court was wrong to dismiss the damages claim at a level of "quantification of loss", without first determining whether the wrongful conduct caused a loss.Their lawyers will tell the court even if the loss cannot be quantified they are entitled to a "reasonable estimate".But the Commonwealth Bank will tell the High Court the shareholders have the wrong end of the stick.The bank argued that the shareholders should have proved the proportion of the share price drop referable to its impugned breaches."The full court found that the appellants failed to make out their case on quantification of loss," the bank's submissions to the High Court said.Glitches led to breachesThe bank said in its submissions to the High Court the problem with the transaction reports started when an unrelated IT problem was being fixed in 2012."Put simply, the cause of the problem was a single IT coding error," the bank's submissions to the High Court said."Once the error and its impact on (threshold transactions) was discovered, it was escalated to senior management, promptly self-reported to AUSTRAC, and rectified."The bank said the second issue arose out of a fraud enhancement program, where an IT error was introduced while updating some accounts."That meant that certain automated transaction monitoring rules were not applied to those accounts," the bank's submissions to the High Court said.The problems were addressed by 2015 and the bank eventually reached a settlement with AUSTRAC, which imposed the fine.At the time, the bank apologised and said it had spent $400 million to fix problems with technology and people.