Nine's writedown was announced in its half-year results on February 23 and pushed a $75 million underlying profit into a $237 million loss for the first half.

The Australian Securities and Investments Commission (ASIC) released a statement on Monday "noting" Nine's decision.

"ASIC reviewed Nine's 30 June 2016 financial report as part of its ongoing financial surveillance program. ASIC raised concerns regarding the value of the goodwill relating to the Nine Network," the statement read.

Nine's shares are trading at $1.04 on Monday, the same as Friday's closing price.

After last week's results, chief financial officer Greg Barnes, who joined Nine in July, said the impairment "was the right thing to do" because of the low share price. Nine's shares have been trading at about $1 since early 2016.

"Write it down and move on," Mr Barnes told Fairfax Media.

Asked if Nine received any input from ASIC, he said, "It would be fair to say that when your market cap, your share price, sits below the book value of your assets per share – which Nine's has done really for the majority of time since it reported its last year's results – that it would get the attention of regulators".

The financial accounts stated Nine Entertainment Company had done impairment testing on its television networks and found "an impairment loss in Nine Network's goodwill of $260 million was required" due to declines in advertising market activity and a fall in earnings.

A week earlier Seven West Media revealed at its half-year results it was reducing the carrying value of Yahoo7 from $201 million to $129 million. It said at the time this was due to a shift "from display to programmatic advertising" as a reason.

It also changed from a "fair value minus cost to sell" valuation to a "value in use" valuation. This means is went from a guess of how much Yahoo7 would be worth after selling, to calculating the value of money actually generated by Yahoo7.

However, ASIC announced a few days later the writedown came following an ASIC review of the 2015-16 accounts.

ASIC is focusing on companies using realistic valuations, particularly in the mining sector and assets "that may be affected by digital disruption". Television networks have lost significant advertising revenue to online ads and social media advertising.

Fusion Strategy director Steve Allen said Nine's writedown might have been necessary because "Nine wrote assets up during its [2013] float, which raised eyebrows".

Television networks did not have the same value they had five years ago, Mr Allen added. However, he believes advertising dollars are returning to free to air.

"We just feel that advertisers' mood has changed towards TV, particularly with revelations that have come out about social media metrics," he said.