Unfortunately it's very difficult to detect, so the best defensive weapon is vigilance. Take a minute to consider any email you receive before following links or clicking on attachments.
If anything at all looks even slightly suspect, do not go any further.
Advise your IT support as soon as you recognise or suspect that you’ve been infected. The signs are usually pretty indicative. You may know as soon as you opened an attachment or followed a link in an email that things weren’t right.
So act immediately - get your computer off the network. No messing about, just yank the network cable out, and then shut the PC down.
If someone else released the virus, then you may notice that shared files on your network are being renamed, or you suddenly can't open them. In that situation, everybody needs to get off the network, fast, until you can identify the machine that started it. Whoever released the virus will have their My Documents encrypted. That's the machine you're looking for. The virus does not spread – it will stay on that machine, encrypting any files it can see across the network, so quarantining the offending machine will stop the encryption marching across the network. Oh, and make sure you have good backups. You'll need them.
Above all, please, please, do not pay the ransom. It only encourages them.
Okay, having an answer on a website you currently can't access may seem illogical, but you may be able to connect via your phone, so we'll go for it anyway. First of all, check if you're the only person affected in your office. If you are, check that you can access your server drives; maybe your network cable has come loose, or you've lost your WiFi connection? If everyone is affected, you'll want to reboot your router in the first instance.
(You may be told to "reset the router", so see the FAQ below). You want to see a nice, steady DSL light showing on the router.
Please do not reboot your file server, unless your IT support specifically ask you to.
It means reboot it ie. turn it off for 5 minutes and back on. Do not, whatever you do, press the reset button (if there is one) or poke the hole marked "reset" with the business end of a paperclip. That will factory reset it and wipe all the configuration settings.
You pull the paper in the direction it feeds. If you pull it backwards, the gears will lock onto it and (a) you could damage the printer, while (b) it's more likely the paper will tear, leaving bits behind and leading the printer to believe it still has a jam.
NO! Whether Microsoft support, "Windows" support, even BT support lately, do not give anyone unsolicited access to your computer, no matter what they say.