In the wake of a major glitch causing nearly four-hour trading halt at the New York Stock Exchange (NYSE) last night, regulator Sebi and stock exchanges in India have initiated an urgent review of the overall risks management and disaster recovery systems of the Indian markets.Top officials said the systems in India are already being upgraded constantly to tackle any unforeseen circumstances but it was decided to take a stock of the situation last night itself when first reports began coming in about the NYSE case. They expressed satisfaction about the systems after this urgent review and said nothing was found amiss.The initial investigations in the US have shown that the 'technical glitch' at NYSE was caused by some 'internal software upgrade' and the regulators and other agencies have so far ruled out any external reasons such as cyber attacks.Incidentally, Sebi earlier this week issued a new set of guidelines for the stock exchanges and other market infrastructure institutions to safeguard their systems, networks and databases from cyber attacks.