A minimum value of -1.#INF or a maximum value of 1.#INF means either negative infinity or positive infinity. Some third party applications seem to allow for values that fall outside the supported range of values for an ESRI GRID. When this occurs the value will be changed to the 1.#INF in ESRI products. As the ArcInfo workstation ArcDoc help states, the range of data values that can be stored as grid values are as follows:
Floating point grids can store values from + or - 3.4E+38 (3.4 * 10 ** 38) to + or - 3.4E-38 (3.4 * 10 ** -38).
Integer grids can store values from -2147483648 to 2147483647 ( -(2 ** 31) to (2 ** 31) - 1).
For integer grids, this information applies only to the VALUE item. An integer grid may have other INFO items added to its VAT whose range of values depends on the item definition.