4. A swollen battery in a MacBook Pro or Air can impinge on the trackpad from below and cause erratic behavior. If you have trouble clicking the trackpad, this is likely the reason. The battery must be replaced.
5. There's a report that a (possibly defective) Thunderbolt Ethernet adapter can cause the built in trackpad of a MacBook to behave erratically. If you're using such an adapter, disconnect it and test.
6. There's also a report of erratic cursor movements caused by an external display that was connected but not turned on.
7. If none of the above applies, or if you have good reason to think your computer is being controlled remotely, remove it from the network by turning off Wi-Fi, disconnecting from a Bluetooth network link, and unplugging the Ethernet cable or USB modem, whichever is applicable. If the cursor movements stop immediately, you should suspect an intrusion.