Be very careful not to open any emails with suspect attachments!
If you do not recognize the sender or are not certain of the content of an attachment, either delete the email and attachment have your IT department check it for you.
Ransomware is a malware that encrypts your files and the coder, malware writer or hacker, then requests a ransom to have your files decrypted.
Once your are infected or your files have been affected, you would have to pay a ransom of US$300 or 300 EUR to have it decrypted. There is no way to reverse this process unless the ransom is paid. We have heard of organisations (schools especially) that have had to pay up to $5000 to decrypt their files.
Although the malware can be removed (by means of anti-malware software such as Trendmicro Titanium), your files will remain encrypted unless you pay for the decryption key. Files will show up as "Corrupted file" or "Unable to open - File is Corrupted", because it has been encrypted.
The malware is propagated, normally via emails. These emails normally masquerade as emails from UPS delivery, resumes, taxation office refunds, bank notices etc. Unfortunately they can also seem to be from friends or known senders who have been afflicted with the Ransomware and whose address book has been used to propagate the offending software.
The best defence is to make sure you have backups of your files but be warned, even though you may have backups in place, it would still be pertinent to advise caution, as it takes time to retrieve files and clean up the systems once the Ransomware has been unleashed on a network.