We've had calls from this number. ajapale is right. It is autodiallers. They tell you they are ringing from computer maintenance dept. I never let them get any further than that. My usual response is that I do not have a computer or that it is not in for maintenance and I do not take "cold calls". They hang up straight away and don't ring back for about a month. If I don't answer, it rings a few times a day until the phone is answered.
I think there is another post about this where they ask you to turn on your computer, go to a website and download something which I understand is pretty harmful to your computer, passwords, online banking, etc.