Bitcoins are once again being targeted by hackers. Business Insider‘s Julie Bort spotted an alert from the U.S. Computer Emergency Readiness Team, which is run by the Department of Homeland Security. That alert is dated last month and warns of the CryptoLocker virus. The virus was spreading like made in the U.K. in November, but apparently it has now crossed the pond and is targeting computers in the U.S.

Bitcoin

“Tens of millions” of computers targeted

The U.K.’s National Crime Agency sent out an alert last month which said that hackers targeted “tens of millions” of computers there. CryptoLocker is actually a type of ransomware, which means the hackers are basically holding your computer hostage. In exchange for unlocking it and restoring it to full use, they want payment. In the case of CryptoLocker specifically, hackers want your bitcoins.

How CryptoLocker works

Here’s how the virus works, the hackers encrypt your computer files, and then there’s a pop-up which tells the user how much they have to pay in order to get their files back. The amount varies from case to case, with some hackers demanding $100, others demanding $300, and still others demanding two bitcoins, which as of right now are worth a little over $1,000 each.

Usually the hackers give the computer owner 100 hours to pay up. Sometimes they restore the files if the ransom is paid, but other times they won’t. Sometimes they demand payment again at some time in the future.

How to avoid getting infected with CryptoLocker

Officials say the majority of the time, the virus is attached to an email, which is often a fake tracking notice from either UPS or FedEx. This is an especially big problem right now because so many people are ordering gifts online and having them shipped to their home. Others are shipping packages to loved ones across the country. The best defense you have against getting this virus is just not to click in attachments to emails. Also backing up your files will help you restore them in the event that something happens to your computer.

Authorities are apparently making progress on shutting down some of the computers which are sending out the emails with the CryptoLocker virus attached. More than 100 of the systems have reportedly been located and blocked, although the virus is still circulating. A police department in Massachusetts even coughed up 2 bitcoins early last month to get their files.