Finally! Twitter has added two-factor authentication, which requires a second check (a verification code sent to your phone) when you sign into the service from an unknown device. This is a much-needed feature for online accounts to prevent hackers from taking over your account (and we've seen that happen a lot, on Twitter especially). Here's how to get this set up and the other places you need to turn on two-factor authentication.

For Twitter, log into your account, click on the gear icon in the navigation bar, and choose Settings (or go to https://twitter.com/settings/account). Next to the Account security setting, check "Require a verification code when I sign in." If that's grayed out, you'll first need to add a phone to your account and then go back to the Settings to turn on two-factor authentication. Learn more from Twitter's announcement.

Where else should you turn on this extra security feature? In a word, everywhere. Most importantly:

• Your email account(s). See instructions for Gmail.
• All financial service accounts (bank, investments, etc.)
• Password-management sites, such as LastPass
• Online storage service providers, including Dropbox
• Microsoft(used for your SkyDrive, Office Web, Xbox, Windows 8 PC login, and more)
• Other social media sites, such as Facebook
• WordPress, if you have a WP blog (see my post on ITworld), other webhosting service, and domain name service providers

Learn more about two-factor authentication here.

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Here's a cool new feature Google has rolled out (in addition to the many other amazing things the company announced at its I/O developers conference): payments via email. Now all you need to do to send someone money quickly is send him or her an email from Gmail.

Google has wrapped Google Wallet, its mobile payment system, into Gmail. To pay someone, the Official Gmail Blog says, you just need to click on the $ icon in the attachment bar when composing an email. Sending money in Gmail is only available on desktop right now, but you can also visit wallet.google.com from a mobile device. To do either, you'll need to set up Google Wallet first.

Just as I was writing this: News that other mobile payment provider Square will also allow sending money via email through a new product called Square Cash.

Looks like we're getting even closer to a wallet-less future.

Adobe's mobile app Photoshop Express is now available for Windows 8 devices, including the Surface and other touchscreen laptops and tablet PCs. The Windows 8 app allows for basic photo editing as well as one-touch auto-fixing, slider controls to enhance images, and Instagram-like filters.

You can also upload the photos from within the app to Adobe Revel to sync them across your Windows devices and other platforms.

As more touch-optimized apps like this roll in each day, Windows 8 tablets potential as a great productivity tool--even in the Metro interface--gets even better.

Also interesting, as the Creative Blog points out, Photoshop Express comes hot on the heels of Adobe announcing it was moving Creative Suite software to the cloud and nixing desktop software.

Download the free Adobe Photoshop Express app for Windows 8 here.

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If you have a Windows 8 laptop, tablet, or desktop PC, you're not limited to just the default themes that come with Windows 8. There are tons of free wallpapers available around the web, but in addition to those, you can use theme packs direct from Microsoft. These are packs of desktop background pictures, window colors, and sounds. New themes are available now with some stunning natural photos of Alaska, New Zealand, and Sweden, as well as a sweet illustration.

In addition to the new themes announced recently, other themes you can download for free from Windows cover all sorts of categories, including panoramic (dual-monitor) themes, animals, movies, holidays, and more.

They're a great way to freshen up your desktop and keep you inspired as you work with your Windows 8 PC.

Related: 8 Things to Know About Windows 8