Encryption Technology
This is the main feature of so-called secure web sites that encrypt data for all transactions. This is only necessary when sending information say as you pay your bill, you would notice the browser if you watch closely shift to some other mode which would become evident due to it working a bit slower than usual. After paying it again reverts to un-secure mode which is faster and allows more users to access the same data you are. Secure transactions are slower for the data is encrypted with a public key which is generated by the sending computer who then sends it along with the data, the receiving computer then uses the same key to decode the information and generates a verification file sending it back, again this is encrypted to verify that the transaction was a success. That confirmation file is the softcopy of the receipt you get when doing online purchses.