You probably can’t stop employees from surfing the Web. You can at least let them know which sites present the worst threats to your system’s security.

A new study from security firm Symantec shows that while pornographic and other illicit sites are dangerous, they’re not the biggest threats out there.

Websites that employees are likely — and innocently — to visit throughout the day have quickly turned into the most dangerous ones to access.

The site categories that you’ll need to be particularly careful around, according to Symantec:

• blogs and web communications

• business and economy

• education and reference

• technology, and

• entertainment and music.

Those sites have the highest likelihood of transmitting some form of malware or virus.