Regulator Sebi is mulling tightening its investigation and enforcement mechanism to check misuse of stock market platform for generating "bogus" long-term capital gains to launder black money. The markets watchdog has also come across cases wherein fraudulent tax benefits have been claimed through trades in some blue-chip stocks, as against the common perception of only penny stocks being used as vehicles for such frauds, a top official said. While the rules provide exemption from long-term capital gains through stock market trades, the government in this years Budget, announced steps to limit such benefits only to "genuine trades" as part of a concerted effort to clamp down on tax evasion through "sham transactions". The regulator is now looking at further steps to ensure such benefits are available to genuine investors only as they are aimed at encouraging long-term investment culture in the country, the official said, while adding that some changes