They are very dangerous people, not only to law enforcement and the BLM and Forest Service, but to ordinary citizens too.
In an article linked in this thread, one Forest Service/BLM employee stated that he/she advised their people in the field to be cautious, that after a bomb went off in a federal office.
In fact, I did some digging on the internet and found that agencies are now advised how to operate more cautiously due to the threat from those militia groups.
In fact, a new pamphlet was issued out (1999) to workers about being more aware of the dangers in their jobs.
http://www.fs.fed.us/t-d/pubs/pdfpubs/pdf00672820/pdf00672820dpi72.pdf
This came on the heels of bombings and threats to Forest Service employees. It's a little known fact that pipe bombs, and pipe bomb makings have been found in National Forests.
I, myself call these people who wish to do harm to others militia groups because normal people don't do these kinds of things. The government doesn't know who was behind the attacks yet.