Simply make sure the locked padlock is displayed on your browser whenever you are transmitting personal data to an e-commerce site. An unlocked padlock means the transaction is insecure and open to hacking. Buy and install anti-viral software for your computer. This software scans your computer for any foreign programs and removes them. Anti-viral software usually requires frequent updates to keep it current, but those updates are usually free and take only minutes to download.
Several sites exist to alert people to scams and hacked sites.
Checking these sites often can keep you updated on the latest attempts to take advantage by hackers and frauds. If you are banking online, make sure your bank is reputable, with a good security record. Before deciding on a bank for online banking, ask questions regarding the security they provide for their customers.