Firefox browser and your banks' internet banking site. If you use windows do not install cracked software, browse sleezy sites or open attachments that are from people you do not trust. Do not communicate personal details with people you do not trust. On linux do most of the same things but since your apps are open source give them a glance over or read sites where people know they prove trust. Then your internet banking should be as secure as the cryptographic protocol that secure your channel to the bank.