Hundreds of thousands of people could be in for an unwelcome surprise on Monday, unless they check their computers now for a global virus that infected their machines last year.

The virus caused by Eastern European hackers will make it impossible to access the Internet.

Facebook and Google are alerting users who they suspect may have infected computers.

The hackers used an online advertising scam to take control of nearly 600,000 computers last year, harvesting information about users.

A temporary fix set up by the U.S. Federal Bureau of Investigation closes down at 0401 UTC Monday.

The FBI has a website where users can find out if their computers are infected and how to fix them — www.dcwg.org.