Facebook and Google are trying to spread the word that hundreds of thousands of people may lose their internet access in July. A computer infection called DNSChanger may ultimately knock them off the internet.
It started when international hackers ran an online advertising scam to take control of computers around the world. The FBI set up a safety net months ago using government computers to keep infected users online, but that system is going to be shut down July 9th, killing the internet for all of those people.
Go to http://www.dcwg.org/ to see if your PC is clean.