I know a little bit about Viruses because I did quite a bit of research on them years ago.
I even checked last night for this particular one that forced multiple *advertiser censored* site hits to an unsuspecting user. This was actually a nasty virus that was commonly going around right around the time of Travis death.
What I suspect is Jodi got this virus herself on her PC, and she knew how she got it, and decided to give it to Travis as a "gift".
There were multiple ways to get it. And many variations of it and names of it.
Infected Screensavers was one way, and sure enough one with crawling bugs was associated with this virus in 1 spot I saw last night on a virus forum.
Another way was by email attachment that was sent through email and opening the attachment.
There were other ways as well to pass the infected payload to a PC.
To answer the question you had, if LE could have gotten Jodi's PC before she broke it, they most likely would have been able to find out she had this exact same virus. I suspect that is why she destroyed her machine.
If they have Travis copy of the hard drive BEFORE any Anti-virus removed and deleted the infection, they may be able to tell if he got it from a screensaver or an email attachment. If anti-virus already deleted the virus, it would be much harder for them to know the delivery method. But its a good question and maybe possible.