Poor old Twitter. It seems the ease and speed of the micro-blogging medium has struck again, raising yet more concerns about just how easy it is to spark off significant real-world reactions that can have potential legal or reputation implications. This week at a US conference the chief executive of Nokia, Stephen Elop, was forced to deny rumours that had originally surfaced on Twitter that Microsoft had agreed a USD19bn takeover of the mobile giant. The rumours directly created a rally in the price of Nokia shares, which had been depressed after the company's profit warning and seemed logical given that there is a growing relationship between the two companies since they signed a strategic alliance in February 2011. The market activity was directly sparked by a tweet, and clearly reinforces that social media presents quoted corporations with a risk from the inadvertent use of or assumptions about material information. In this context materiality really means "is it likely to influence someone to buy or sell shares?"  Stock market regulations are extremely strict about this seemingly simple question - and can penalise companies who do not ensure there is correct and equal access to any such information for all potential and current investors. In a social medium it seems that the risk doesn't even only come from mentions of a brand name - in this case, Russian blogger and mobile industry analyst, Eldar Murtazin, allegedly sparked off the real-world buying and selling of stocks through this short post: "One small software company decided last week that they could spent 19 bln USD to buy a part of small phone vendor. Thats it."  Initial Retweets (82 of them) were followed by more repeats, rumour and speculation - firstly about the question and then later about the denial. It spread throughout national and international media like wildfire. PR professionals in major corporations (and, one hopes, in any agency which works for a blue chip or publicly listed client company) are painfully aware of the vital importance of ensuring that communication about anything deemed 'material' to the stock price goes out in a controlled and exactly timed manner to every potential interested audience.  However, even speculative or casual comments can do the job. In this case, there's actually no question of an internal staffer post having created an issue, but it does raise the spectre that any casual social discussion about things with material implications could cause real issues. It would also suggest that the social media policies, training and advice to staff within companies that must comply with stock market regs are even more vital than they have perhaps realised before.