Already fierce rivals, Baidu (BIDU -0.1%) and Qihoo (QIHU -4.8%) appear set to compete even more. Marbridge Consulting observes Baidu has released a beta version of a PC security/maintenance app called Baidu Guard, which would compete against Qihoo's very popular 360 Safeguard software. The release comes a few months after Baidu unveiled antivirus software that also competes against Safeguard. Qihoo, which often bundles its browser and security software, claimed 457M monthly users for all its products/services as of March. Mobile security software users totaled 275M.