Creating a Home Made virus is easier than you would expect when you use plasmid techniques pioneered at the University of Wisconsin.
While you can create a new virus from scratch, it is much easier for the novice to take the open source approach and modify an existing virus to accomplish your own ends. Very few decent cell-level debuggers exist right now.
This system utilizes plasmids. A Plasmid is the same as a virus, but is lacks that characteristic protein coating and therefore cannot move between cells in the manner that virii do.
Due to their soft-shelled nature, a substrand of DNA may be grafted into a plasmid host if both the host plasmid and the foreign DNA have recognition sites for the same restrictioned endonuclease. What this means is that since certain nucleotides can only bond to certain other nucleotides, your substrand must match up with break in the host plasmids' DNA structure according to the constraints of this DNA Base rule. If done correctly, that substrand will become, transparently, part of the plasmid structure using the action of DNA ligase.
Using this technique, a new plasmid that has the grafted DNA as an insert is created. However, if the base pair combinations are incorrect, the entire string inside of the plasmid will be non-viable.
Then, this new plasmid can be introduced into a bacteria cell where is will reproduce itself using the traditional techniques that viruses use. This also forms the basis of DNA cloning.