The obvious reason and what I would assume is most likely is the frequency of these names in at least the United States:
Rank Name %
1. Smith 1.006
2. Johnson 0.810
3. Williams 0.699
...
11. Anderson 0.311
Smith is the most common last name, meaning there would be a lot of them. I had also assumed having similar names would make them more difficult to track in a hacker world. Do any of these assumptions make sense? Many movies shy away from using incredibly common last names, although I have no source for this.
Is there a reason the Wachowskis chose Smith and Anderson for the characters' names in The Matrix?