Most virus infection comes while using USB with computer. USB device is used to carry data through PC and office or from market to PC. Public places where we can use computers such as internet clubs, offices, markets where there is local network area is enabled are considered to have potential virus carriers where USB/Flash drive can easily get infected and later on can cause data loss/virus/malware/adware infection in your home PC. Be careful enough while using USB drive while outside to avoid virus infection. There is a way to be safe from even infected USB while using it.