Depends just how securely you want it wiped.
Deleting merely removes the file header info, making it unrecognisable to the OS. Even then, once it's been overwritten, it's possible to recover data by someone who knows what they're doing, with the right tools. I've heard the computer forensics chappies and chappesses that work for the police can do this, sometimes, with files that in some cases have been overwritten more than once. This is not a worry with malware/virii, once it's been deleted/overwritten it's not likely to ressurect itself. But for secure deletion, say, of "sensitive documents", eraser, referred to above, offers a 35 pass overwrite of free space, or any file, or folder. It's referred to as the Gnutman (sp?) for the chap who designed it.
That's got to be as secure as it gets, for just your regular paranoia.