A lock comprising: a cylindrical plug having an axially-extending keyway adapted to receive a conforming key; a plurality of tumbler pins disposed within radially-oriented tumbler pin holes formed in said cylindrical plug and adapted to control rotation of said cylindrical plug, wherein said tumbler pins are constructed and arranged to be engaged by a properly configured key inserted into said keyway and to be positioned by the key within their respective tumbler pin holes so as to permit said cylindrical plug to rotate; an auxiliary locking pin disposed within said cylindrical plug and moveable between a first position in which a portion of said auxiliary locking pin extends out of a hole formed in an outer wall of said cylindrical plug and a second position in which said auxiliary locking pin is retracted into said hole, wherein said tumbler pin holes are parallel to each other and wherein said auxiliary locking pin includes a shaft that is oriented within said plug so as to be generally parallel and laterally offset to said tumbler pin holes; and a slider disposed within said cylindrical plug and moveable in an axial direction between a first position and a second position, said slider being constructed and arranged to be engaged by a slider contact surface formed on a key blade of a cooperating key inserted into said keyway to move said slider from the first position to the second position, wherein said slider is operatively inter-engaged with said auxiliary locking pin such that said auxiliary locking pin is in its first position when said slider is in its first position and said auxiliary locking pin moves from its first position to its second position when said slider is moved from its first position to its second position. a cylindrical plug having an axially-extending keyway adapted to receive a conforming key; a plurality of tumbler pins disposed within radially-oriented tumbler pin holes formed in said cylindrical plug and adapted to control rotation of said cylindrical plug, wherein said tumbler pins are constructed and arranged to be engaged by a properly configured key inserted into said keyway and to be positioned by the key within their respective tumbler pin holes so as to permit said cylindrical plug to rotate; an auxiliary locking pin disposed within said cylindrical plug and moveable between a first position in which a portion of said auxiliary locking pin extends out of a hole formed in an outer wall of said cylindrical plug and a second position in which said auxiliary locking pin is retracted into said hole, wherein said tumbler pin holes are parallel to each other and wherein said auxiliary locking pin includes a shaft that is oriented within said plug so as to be generally parallel and laterally offset to said tumbler pin holes; and a slider disposed within said cylindrical plug and moveable in an axial direction between a first position and a second position, said slider being constructed and arranged to be engaged by a slider contact surface formed on a key blade of a cooperating key inserted into said keyway to move said slider from the first position to the second position, wherein said slider is operatively inter-engaged with said auxiliary locking pin such that said auxiliary locking pin is in its first position when said slider is in its first position and said auxiliary locking pin moves from its first position to its second position when said slider is moved from its first position to its second position.