Those dodgy pictures on the women in lycra thread.

[Canrider]

They would have to be a pretty determined expert to do this, right?

No, not necessarily. For example, the temporary files IE uses to store the files are given code names consisting of a combination of numbers and letters, just so IE can keep them all straight without having to worry about the original filenames. That makes the files in the temporary folder anonymous at first appearance, but they can still be opened an looked at--all that's required is patience to go through them one by one. The size of the files and things like that can also give clues as to the contents.

If you delete them from the temporary folder, the data is still there, just the filename has been changed. Utility programs exist which can undelete deleted files, again just by changing that first character in the filename back from the 'DOS ignore this file' character the deleting process changes it to.

Defrag (IMO) may or may not do very much. It depends on how full the hard drive is, where the block containing the unwanted data are, and whether the defrag overwrites other data to those blocks or not during the course of its work.

 

[Globalti]

I think I'll stop worrying about this now. Our IT bloke wouldn't have the time to trawl through all the thousands of images I've viewed on URBEX, Land Rover, cycling, DIY, VW/Audi, weather, skiing, Ebay, not to mention all the other trash I look at while wasting time at work.

I hope.

 

[Canrider]

Aah, the plot thickens.
Since you're most likely dealing with the Internet through a networked PC, well, that network can be set up to monitor traffic between the Internet and your office computer. There are places of employment where even some banner ads (the T3 girlie ones spring to mind, from the C+ days) can get you in trouble. Hence the often-seen mention that certain sites or threads are NSFW (Not Safe For Work).

Which, incidentally, would be nice if people added to threads here in the Cafe. I've seen a couple recently where I had to think hard before clicking (actually, before deciding not to click), as I could just imagine that I'd wind up with unwanted pr0n coming down the line.