There is no such thing as job security anymore. Outsourcing and a plethora of out of work people tips the industry in favor of the employer. People are brought in, used as upper management sees fit, and let go just as soon as they are no longer needed.
Case in point, a friend of mine recently started a job where he was told it would be a contract to hire job. He believed they would hire him without a doubt. They had him work on a single project for two months. Literally as soon as he finished a prototype and dropped it off at the mail room, he was called into him managers office and let go. My friend found out later that they only wanted him there to work on that one job.
I've experienced it a few times myself. I finish a project, they no longer need me, and I'm given the walking papers. Every single one of my friends have dealt with this same issue. See "The workforce reduction."
It's also a bad sign when every single company that is hiring bring in candidates as contractors for 6 to 12 month terms. If they do that, it's almost certainly because they expect to expunge you are some future time.
What do you do then? Just move on to the next contract. Treat every job as if you are only there briefly to gain some experience for the next place. In fact it can be fun, one month you are working on robots, the next UAVs. Variety is the spice of life, as the cliche goes. So, embrace the new career industry knowing exactly what it is, temporary.
Also, in the United States, unemployment has been extended so many times that some people have been on it for over 2 years. If that isn't an indication of trouble, I don't know what is.
Cabe
PS. To directly answer your question, between 3 months to 2 years. I do a lot of contract work.
