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Historically, Mac OS X enjoyed a near-absence of the types of malware and spyware that affect Microsoft Windows users. Mac OS X has a smaller usage share compared to Microsoft Windows (roughly 5% and 92%, respectively), but it also has traditionally more secure UNIX roots. Worms, as well as potential vulnerabilities, were noted in February 2006, which led some industry analysts and anti-virus companies to issue warnings that Apple's Mac OS X is not immune to malware. Increasing market share coincided with additional reports of a variety of attacks. Apple releases security updates for its software. In early 2011, Mac OS X experienced a large increase in malware attacks, and malware such as Mac Defender, MacProtector, and MacGuard were seen as an increasing problem for Mac users. At first, the malware installer required the user to enter the administrative password, but later versions were able to install without user input. Initially, Apple support staff were instructed not to assist in the removal of the malware or admit the existence of the malware issue, but as the malware spread, a support document was issued. Apple announced an OS X update to fix the problem. An estimated 100,000 users were affected.

When did Mac OS X experience a large increase in malware attacks?
early 2011