Did I Get Hacked?

As a rule, never open an email attachment that you are not specifically expecting from a trusted source. This is how some of the biggest hacks, including the Target breach apparently happened. An employee of a Target contractor opened an email attachment which contained a keylogger rootkit. The malware was subsequently able to capture the contractor's Target login credentials, which allowed hackers a doorway into their corporate servers.

AV would not necessarily stop it as there are so many variants of zero-day malware, and the user essentially gave permission to install it. As an aside, this would likely not have happened if using a non-admin account without install privileges on a PC.

The two most common malicious malware contained in email attachments are keyloggers and ransomware. Both extremely dangerous. With new cryptoware now using a delay tactic before it actually encrypts files and demands a ransom. Both on PC and Macs.

I would do as suggested, and backup all key files. And do not use the computer until it has been thoroughly cleaned by multiple AV applications. Though note that security experts state they would not use any system which has been infected by "known" malware, as they cannot trust malware has been completely removed. Especially, where rootkits are involved.

Best practices would be to thoroughly wipe the drive and reinstall from a clean system image.

Malwarebytes will clean your computer. Make certain you update your version or download the latest version.

You'll then be good to go.

https://www.malwarebytes.org/

might also be scareware. i just fixed a friends computer hit with one of these.

see http://www.kadansky.com/files/newsletters/2015/2015_08_31.html
fir example of scareware

Let's see if your AV program is working. I think your email program should have warned you. Gmail does. It should have marked it spam.

As I recall malwarebytes has been working on anti ransom software and a beta version #5 is currently available. It's not incorporated into their std product. Worth a look.

What OS a you using?

Good advice
Disconnect from the internet connection
And backup your files/documents and pictures
Do NOT do a whole drive backup... Do NOT backup the infection

In three days you will find out. Put all files you absolutely need on a thumb drive. Do not leave it in the computer. Chances are high you have been hit with the Ransomware virus.

Any time you get an e-mail that looks suspicious or "funny", click on the name of the sender to get a detail of the e-mail address, even if that name is familiar. Often the e-mail address is not the address of the name appearing on the e-mail.

Can't help with what to do now.