how about smith? is he the one? NO! Smith is a program that was "destroyed" by Neo, thus being obsolete. Oracle states that when a program is replaced, it can stay in the matrix or return to the source.
"...and then somthing happend. Somthing I knew was impossible but it had happend anyway...you destroyed me. After words I knew the rules, I understood what i was supposed to but I didnt....I couldnt. I was compelled to stay, compelled to disobey."
Smith has become nothing more than a rouge program, a virus in a sense.
"The function of the One is now to return to the Source, allowing a temporary dissemination of the code you cary, reinserting the prime program. After which, you will be required to select from the matrix 23 individuals--16 females, 7 male--to rebuild Zion. Failure to comply with this process will result in a cataclysmic system crash, killing everyone connected to the Matrix, which coupled with the extermination of Zion will ultimately result in the extinction of the entire human race."
This cataclysmic system crash may be Smith himself since he is pretty much spreading his virus to EVERYONE in the matrix. Thats what I think is Smiths "Purpose"