There are too many bad things in emails or malware or more to the point RANSOMEWARE that will encrypt your docs and demand payment.
If they click on attachments then they may only learn this the hard way. There is no single cause or cure.
Here's a video on a recent SCAM.
http://www.youtube.com/watch?v=J1U4U2rHLFo
Bob
Hi, I have today been looking at a friends PC who clicked on some attachment in an e-mail and something has run and corrupted all his docs.
All JPG, DOC, XLS, PDF, LNK (IE favourites) will no longer open (says file is corrupted) and have been made read only. Whatever ran has only affected all docs in the 'Documents' and 'Favorites' folder. Even in IE9 clicking a link in favourites brings up a corrupted message. Creating an saving new Word/Excel docs is fine.
Fortunately there is a full data backup from 2 weeks ago, but I was wondering if anyone new what might have run on the PC?
Chowhound
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