Yep - virus software updates itself daily - in addition, when files started being a problem on the USB I suspected a virus, manually updated the virus software and ran it over the USB as well as my computer - both were 'clean'
Then I also ran them both through some malware software - some cookies deleted from the computer, but the stick was clear (as was the other external drive which is now a problem).... Perhaps that was where the bug was? But I would've thought that the virus software should've picked it up too, shouldn't it?
Although it started with pdfs and illustrator files, I did lose other types of files as well (including word, excel etc)
Since I deleted the Reader (which was AFTER I'd run the virus software), the spreading corruption problems have stopped (I haven't lost any more files/documents) and I can now open and reopen pdfs and Illustrator documents without any problems - though it may just be a coincidence that the two things started and stopped at the same time...
If it is/was a virus that is now gone (or appears to be), is it possible that I might be able to recover them? Can you give me any tips for what I should look for in recovery programmes/software?