5. A signature matching engine stored in units of substrings to which signature strings for distinguishing harmful packets included in introduction traffic are tokenized, comprising: an internal memory block having a first memory table including a first substring included in both a first signature string and a second signature string, and having a memory table that includes a second substring from among substrings of the first signature string, wherein the second substring was stored in the internal memory block when the first memory table including the first substring was already linked to a memory table including another second substring from among substrings of the second signature string, and wherein the memory table that includes the second substring is linked to the first memory table; and an external memory block having stored therein a memory table that includes a substring from among substrings of a signature string, wherein the substring stored in the external memory was stored in the external memory when a substring previous to the substring stored in the external memory was not already linked to a memory table of another substring.
5. A signature matching engine stored in units of substrings to which signature strings for distinguishing harmful packets included in introduction traffic are tokenized, comprising: an internal memory block having a first memory table including a first substring included in both a first signature string and a second signature string, and having a memory table that includes a second substring from among substrings of the first signature string, wherein the second substring was stored in the internal memory block when the first memory table including the first substring was already linked to a memory table including another second substring from among substrings of the second signature string, and wherein the memory table that includes the second substring is linked to the first memory table; and an external memory block having stored therein a memory table that includes a substring from among substrings of a signature string, wherein the substring stored in the external memory was stored in the external memory when a substring previous to the substring stored in the external memory was not already linked to a memory table of another substring. 8. The signature matching engine of claim 5 , wherein, when the memory table including the substrings is stored in the internal memory block, the memory table is provided in the address of the internal memory block matched to the hash value of the substring.