If you — or ASIC or the ASX — are looking for another example of well-informed trading affecting stock prices ahead of stockmarket announcements, look at yesterday’s 5.3% drop in the price of construction giant, Leighton Holdings to $42.36 ahead of its 2008 profit announcement and a share issue rumoured at $800 million.

Another example is CSL’s profit announcement yesterday and its $3.6 billion acquisition of US based company Talecris Biotherapeutics Holdings, which has been preceded by a 10% rise in the CSL share price from last Friday. It now sits at $39, within 90 cents of its all-time high (adjusted for last year’s 3 for 1 share split). The company revealed a solid rise in earnings and an equally upbeat outlook for the coming year.

The rise in the value of the company added more than $1.9 billion to the company’s market cap and enabled the $1.5 billion share issue now being placed with big shareholders to be done at a more attractive price.

And then there’s the questionable trading in ports and rail group Asciano ahead of the equally surprising $2.9 billion offer from TPG and a partner. That trading over about a week pushed the share price up 20% ahead of TPG revealing its offer. The offer was $4.40 a share, the share price pushed through that in pre-trading and then jumped to $4.83 or thereabouts the day it was announced.

The pre-trading in Leighton came despite the market being confident in the company’s forecasts of a 30% rise in profit for the 2008 year. This morning Leighton shares went into what could be a four day trading halt. The details of the issue, its probable size and the brokers involved were in the pages of the AFR this morning — why wasn’t it released to the market as a whole last night?

Why do we see this sort of “informed” trading? Because market security is not up to scratch bad when someone wants to alter share prices to someone’s benefit. And those doing it, leaking the information to mates, or doing a spot of quiet trading on their own, know they have a better than average chance of avoiding any action.

These are just three of examples of questionable price movements in trading ahead of announcements, or the dumping of shares (or buying) by insiders around announcements. It’s more dangerous to market integrity than the activities of hedge funds and short sellers.