On November 30, 2016, the IT security company Check Point revealed that over one million Google accounts were compromised by the Android malware "Gooligan". The malware can be installed onto your Android device from legitimate-looking apps from the Google Play store. You can check to see if you account was compromised at the the following URL:
Malicious software is any software that brings intentional harm to a computer system. Malicious software can take part in a wide variety of forms which could steal protected data, delete documents, or add unwanted software.