How can I protect debit card info online?

I make a lot of online purchases, always on legitimate websites that are supposed to be secure. I also pay a lot of my bills (cell phone, utilities, etc) online. Recently someone got a hold of my debit card information and wreaked havoc on my account. I had to dispute a TON of charges they placed. I got all my money back but I wanted to know how I can protect my info best - is there a good type of software to download?