There are many studies that can be found that show conclusively that having your data hosted online with a secure service provider (ex: paypal, quickbooks online, etc.) is MUCH safer than having your data on your personal pc.
This is because the companies that run these services are diligent about security. They have many hardware and software systems in place to insure the utmost security for their systems. Your data is MUCH safer on their well protected system than on your poorly protected (and probably spyware-ridden) home/office pc.
Here’s the problem though:
You access their website using your poorly protected pc… 
The problem with that is the existence of keylogger and screenlogger programs.
These programs monitor your keystrokes and/or take pictures of your screen.
They can capture your keystrokes as you enter your username/password; they can record your screen as you look at confidential information on a secure website.
I have been long interested in overcoming this security threat for my own business (I am a paranoid person by nature) and look at much information on the subject.
Unfortunately it is very difficult to overcome a keylogger/screenlogger. On the bright side an attach is probably not very likely. But that doesn’t make me sleep any better at night.
Here is some information I just found that might give me and you some new tactics in staying safe:
http://www.wilderssecurity.com/showthread.php?p=1534643
Did I scare you?
There are always risks in life.
Email me if I have really worried you or take a deep breathe and then educate yourself by searching for more info about this online.
Knowledge and handling the situation overcome fear.