Operating systems of all kinds are under assault, but the prime target is Windows, because the vast majority of PCs worldwide use that operating system. If you use Windows, hackers have you in their cross hairs.

Luckily, there's plenty of free software for Windows that can help protect your privacy and security. I'm not talking about anemic, underpowered applications. I'm talking about industrial-strength tools that can do everything that expensive security software does.

With all the free stuff out there, which software should you choose? I've selected 10 of my favorite programs that can protect your privacy and security. Download and install them, and you'll be far safer against all the nastiness out there.

Secunia Personal Software Inspector

Some of the biggest security holes in your PC aren't directly related to Windows — instead, they're in the applications you run. As often as not, that's how hackers and crackers can get into your PC. For example, in the recent "Pwn to Own" hacker challenge, it was application vulnerabilities, not Windows Vista itself, that allowed hackers to crack Vista.

The best way to protect yourself from this problem is to keep your applications updated with vendor-issued patches. But you don't want to spend your life cruising the Web, looking for updates for every app you use.

Instead, get this freebie that does it for you. As a security vendor, Secunia keeps track of software vulnerabilities and available patches. The company's Personal Software Inspector (PSI) scans your PC, downloads a current vulnerabilities file, and alerts you to any software on your machine that is missing security patches. It also warns you if any software is out of date and no longer supported by the vendor. Out-of-date software no longer gets security patches, and so may be more vulnerable to hackers.

When you get a list of insecure software, you can get more details about each piece of software, open the folder where the software resides, or download a patch. Click the + sign next to the software, and you'll get even more details about it, often including links to any tools for uninstalling the software. You also have the choice of having Secunia constantly monitor your software use and notify you when patches are available.

Secunia says that some programs require tedious or confusing patching procedures, so by default it starts in a mode that shows you only "easy-to-patch" programs. It's a much better bet to have Personal Software Inspector tell you about all applications that need patches, not just ones that are easy to patch. To make the change, select Settings and uncheck the box next to "Show only 'Easy-to-Patch' programs."

Note that Secunia PSI is free for home use, but requires payment for business use.

SendShield (beta)

Microsoft Office documents often include data that can compromise your privacy or that you don't want others to see, such as hidden text or cells, document revision history, names of document authors and reviewers, and so on. When you send someone a document, they can easily see that information by viewing the version history and the document's properties, and in other ways.

It can be time-consuming and impractical to remember to review every document you send out via e-mail to make sure it doesn't contain privacy-compromising information. Instead, get Unedged Software's SendShield.

Whenever you send PowerPoint, Excel or Word documents via Outlook, it examines them to see if they have any of private information. It then details what it finds and lets you remove the information with a single click. It deletes the information only from the copy of the file you send via e-mail, not the original on your hard disk.

You can also have the documents turned into PDFs and sent that way instead of as Office documents.

SendShield is in beta, and for now is free. However, when it gets out of beta, there is a chance that it will become for-pay software. (The company provided no details on timing or pricing.)