Hello,
I would recommend to anyone getting a used computer (and personally, I do this for *any* computer that becomes mine... new or used) and rebuild it from scratch. Only by doing this, do you know what programs are on that machine, and you alone are responsible for configuring security on it.
I bought a used laptop from a pawn shop several years ago too. Took it home, and the first thing I did was repartition and reformat the hard disk.
You never know what hidden goodies / problems are lurking around. There might even be logical disk drive damage...
Christian