Archie, since you seem to know Jacobs and his work so well.... Why does Jacobs fear that hybrids were/are out to get him and that hybrids sent instant messages threatening him?
On a general point, many hundreds of people know DJ as well as or better than I. Most however don't bother to post on internet forums (probably have better things to do with their time like seriously researching the ET issue).
However on to your question: there is a deep issue here with a lot of history behind it from multiple sources. At least two well-known researchers in the UK have published evidence of what we might call human-looking alien/possibly hybrid activity and interaction here - one talked about his direct personal experience on a paracast a while back. Some of their information has not been made public. I don't know if DJ knows all the details of these encounters and interactions, but I doubt it. I also have some personal evidence from outside the USA not likely to be published anytime soon due to confidentiality issues. I know this to be real, in some way at least.
Let's speculate for a moment. Let's say there is something to this. Let's say that we give some credence to the weight and consistency of evidence over the past 50 years (and more) of seeming interest by apparently non-human agencies in replicating/breeding/interfering with human genes and creating hybrid/transgenic beings for whatever purpose. Reproductive procedures. Sperm extractions. Missing pregnancies. Hundreds of reports of tiny embryos gestating in tanks. Human abductees being encouraged to bond with and hold tiny babies. Reports of infants, older children, young adults. Reports of "human-looking" ETs, possible hybrid/transgenic beings, interacting with us.
If there is anything in all this, is it likely that the military and intelligence services of the world would take a serious interest in this whole issue? Damned right, it's likely. There is strong and peristent documented evidence of interest in the whole ET issue. The Coalition for Freedom of Information, for example, had to work for years to get the CIA and the USAF to release a ton of classified stuff about the Kecksburg crash. Finally, the information was ordered to be released by the courts. If there is some kind of infiltration program going on (still speculating here folks) this would be right up there as numero uno vital international security issue by those dealing with it. Nothing else would come close. Secrecy, in these circumstances, would almost certainly be total and any knowledge about it confined to a very small number on a strict need-to-know basis. These agencies would also be a prime target for infiltration. They might also spread deliberate disinformation to muddy the waters and keep people busy with irrelevancies and BS to bury the truth and keep people away from it. There's plenty of evidence for this, too.
Tom made some good points about a missing trillion dollars from the US defence budget. This was reportedly discovered by the GWB administration on taking office in January 2001 and reported by Donald Rumsfeld to the press in February 2001, and the amount was actually two trillion, not one. Where did all this money go? It's hard to just lose two trillion dollars, and it's apparently untraceable. Black budgets, to manufacture technology to combat the ET threat? The most likely candidate, according to many. As has been said, Reagan mentioned the ET threat five times in speeches, against the wishes of his speechwriters. Clinton referred to the issue on several occasions. The whole issue of public disclosure/secrecy is oft debated but there may be very good and sound reasons to work in secret and try to keep the lid on the whole thing - for now.
So, DJ receiving threatening instant messages: see this in context. People with apparent interactions with human-looking ETs write to him, call him, try to get in touch with him all the time ("Emma Woods" is only one of many thousands, but the only one in 20 years ever to ferment trouble). This continues, even after the disinformation campaign, which will come and go with no effect on the phenomenon, or the weight and frequency of reports. DJ is seen to have a special interest in the subject, has studied it and been close to it for 30 years. He knows a lot about the issue. He's not the only one of course, but he's out there in the public eye - so more potentially problematic, even dangerous, to any potential takeover plan, as he doesn't keep his mouth shut like the security agencies do. He might very well be threatened - for real. Has anyone considered that?
The whole area of how these reported hybrids/transgenics/human-looking ETs/co-opted humans/MIBs and the rest behave is a large and complex one. Books can be written about the detail, and probably should be.
What do I think about DJ being targeted by so-called hybrids? I think, knowing what I know, having experienced what I have experienced and having seen the evidence that I have seen, that it's likely. Can't prove it, don't know for sure. But it's likely true.