The Conficker/Downadup worm managed to slither onto millions of PCs worldwide at its height, but after it initially infected a computer it only really acted to spread itself, and didn’t cause further harm. Until now.

Symantec reports today that it has found a new variant of the virulent worm that will identify antivirus software or security analysis tools running on the infected PC, and attempt to shut down those programs. This is a strong signal that the worm’s mysterious creators haven’t abandoned their creation in the face of worldwide attention, as some in the industry have theorized, but may still have plans to make a buck off their work.

To protect against the Conficker worm, first make sure you’ve installed the patch that closes a targeted hole in the Microsoft Server Service. Next, protect any network shares and administrator accounts with a strong password, as Conficker will try to guess easy ones.

Finally, you can block the worm’s third infection, which hijacks thumb drives and other removeable media, by disabling Autorun on Windows. PC World has a download available that can automate that step for Windows XP users, and Microsoft has posted manual instructions.

Now this: Mac malware is now circulating across the Net via pirated copies of Apple’s new iWorks software.

The “iServices.a” Trojan hitchhikes on iWork ’09′s installer. The installer for the Trojan horse is launched as soon as a user begins the installation of iWork, following the installer’s request of an administrator password.

Once the Mac is infected, the Trojan phones home to let daddy know it arrived safely and is awaiting further instructions. Since then, the same bit of viral nastiness — dubbed OSX.Trojan.iServices.B — has begun showing up in pirated copies of Adobe Photoshop CS4, according to Macworld.

Glass-half-full types can view this as further proof of the Mac’s success; it’s now installed in sufficient numbers to be worth the attention of botnet herders. Also: That room full of manure is sure to have a pony inside.