Commonwealth Bank in 2012 took a further write down on its investments in stockbroking subsidiaries acquired during the years of the equities boom.Accounts for Commonwealth Securities show it took an impairment of A$17 million on subsidiaries during the year to June 3012. CBA took a much larger impairment of $120 million in 2011.The impairments most likely relate to the business formerly known as IWL and acquired in late 2007 (and known before that as InvesorWeb).CBA paid a notional value of $373 million for IWL at the time with around half of the purchase paid in the bank's shares.Even with the impairment CommSec reported a rise in net profit, to $78.8 million from $58.2 million.CommSec said it had 1.79 million customer accounts at June 2012, a rise of three per cent over the year.