Spyware is also a concern for Microsoft with regard to service pack updates Barry Goff, a group product manager at Microsoft, said some spyware could cause computers to freeze up upon installation of Service Pack 2. Spyware and adware are a continuing problem on Windows XP and other versions of Windows. If a user tries to run a program downloaded from an untrusted security zone, Windows XP with Service Pack 2 will prompt the user with a warning. To discourage users from running such programs, Service Pack 2 includes the Attachment Execution Service which records the origin of files downloaded with Internet Explorer or received as an attachment in Outlook Express.

Notable worms of this sort that have infected Windows XP systems include Mydoom, Netsky and Bagle. A user who opens the attachment can unknowingly infect his or her own computer, which may then e-mail the worm to more people. Many attacks against Windows XP systems come in the form of trojan horse e-mail attachments which contain worms. Increasingly widespread use of Service Pack 2 and greater use of personal firewalls may also contribute to making worms like these less common. Patches to prevent both of these well-known worms had already been released by Microsoft. In May 2004 the Sasser worm spread by using a buffer overflow in a remote service present on every installation. For example, in August 2003 the Blaster worm exploited a vulnerability present in every unpatched installation of Windows XP, and was capable of compromising a system even without user action.

Microsoft stated that the release of security patches is often what causes the spread of exploits against those very same flaws, as crackers figure out what problems the patches fix and then launch attacks against unpatched systems. Windows XP Home Edition also lacks the ability to administer security policies and denies access to the Local Users and Groups utility. If the administrator's account is compromised, there is no limit to the control that can be asserted over the PC. Nicholas Petreley for The Register notes that 'Windows XP was the first version of Windows to reflect a serious effort to isolate users from the system, so that users each have their own private files and limited system privileges.' However, users by default receive an administrator account that provides unrestricted access to the underpinnings of the system.

Windows XP has been criticized for its vulnerabilities due to buffer overflows and its susceptibility to malware such as viruses, trojan horses, and worms. Criticism of Windows XP deals with issues with security, performance and the presence of product activation errors that are specific to the Microsoft operating system Windows XP.

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