Regarding the second part of the question…
…for most people, if you need to clear out evidence of your single-handed surfing habits, you just need to clear your browser history, delete temporary internet files and clear cookies.
It’s not foolproof, in two main ways – firstly, if you’re surfing via a network connection then there may be firewall hardware and software that is monitoring or recording all activity. The software they’re selling in that email can’t do a damn thing about that.
The second ‘but’ is the one that your email is trying to capitalise on. When files are deleted, they’re not actually erased from your hard disk. All that happens is that the operating system flags the portion of space that the file once occupied as available for re-use.
If you use the PC a lot, or have only limited hard disk space, then there’s a decent chance that you’ll overwrite that portion of space with something else.
Even then, that may not be full deletion, since the file you overwrite the space with might not be as big as the one that previously occupied it. Space on the disk is broken down into fixed-size chunks to make it easier to manage, so you might overwrite a file that once occupied the whole of a chunk (or ‘cluster’) with one that doesn’t fill it. The ‘leftover’ space will not be overwritten.
There are a number of programs available that can read these fragments, whether images or text. This kind of forensic software is usually hugely expensive and used only by law enforcement authorities and fraud investigators. I have two of the main forensic programs – Vogon and EnCase on my work laptop, although my experience with using them on fraud investigations has been limited to introductory training only.
So-called ‘evidence eliminator’ software (one of the brand leaders is named that) purports to use various techniques to prevent forensic software from working properly. I don’t know the details, but I believe they do things like defragment your hard disk repeatedly, which causes the operating system to re-order and re-index the files more efficiently. This necessarily involves files being moved and rewritten, destroying old ‘deleted’ files. If you were really worried, you could try defragmenting your drive yourself repeatedly without special software, but it’s no guarantee and it can take a long time.
Unless you think someone has reason to scan your PC for something very dodgy (child porn, fraud evidence) then I wouldn’t worry too much. Nobody will be running forensic software on your PC unless they have good reason to. Besides, I wouldn’t trust software in a junk mail to do anything good at all – there are plenty more reputable sources.
I hope (a) that that helps and (b) that that was accurate. Sailor, anyone, confirm this?