if ...you visit a cyber cafe and find any black pin attached to your CPU as shown in the picture, kindly do not use that system. This pin is actually a connection which saves all your data you enter in the system.
Thus it's a risk to your privacy over internet. Risk to your email account password, Facebook password, internet banking account passwords or any data you enter.
It's a hardware key logger & is very powerful. It records each and every action of your system.