My computer system (can choose between Ubuntu, Mavericks or Win 7 operating systems) is powered on 24/7, I do not own a webcam but would buy one if I could monitor the room my computer is in via mobile phone, while I am away, preferably Android based.

Can anyone fire me ideas?

Any software that can alert me when motion is detected?

This would work with Mavericks. The software is well done and easy to use, but I have not tried the phone interface. The motion detection is highly configurable so you don't get any false alarms.

http://www.bensoftware.com/

Why not just install an ip cam? then u can look at recordings, have alarms sent to your phone or even take control of the camera with your mobile from anywhere in the world, ip cams designed for indoor use are quite cheap and easy to set up.