IDG Answers is a community of experts who are passionate about technology. Ask a question or answer one below.
One way to tell is by observing your phone's behavior both objectively (check your data plan usage from your cellular provider and compare it to previous months) and subjectively (does it seem slow? does it seem to be running a background task?). Another way is to run a program called Root Checker to see if Root access has been enabled on your phone. You may also wish to check with your ISP to find hints for dealing with your specific model. It may be possible to perform a reset on your phone to clear out any malware you've unknowingly installed.