The letter was signed by someone calling themselves Moinuddin. It was addressed to police, and published by local newspapers Friday. It warns that there will be bomb blasts on New Year's Eve at a five-star hotel and at the home of Karnataka state's chief minister.
Police say they do not know if the threat is real, but they have stepped up security and say they are taking no chances.
Officials say Wednesday's attack on the science conference, in which a gunman sprayed bullets indiscriminately at delegates and killed one professor, M.C. Puri, was likely the work of militants.
Some information for this report was provided by AFP, AP and Reuters.