Security experts say attacks may be a sign of things to come as attackers home in on Windows XP. One-fifth of all operating systems in use today are Windows XP machines, Microsoft says. There will be no more patches for the 12-year-old operating system as of April 8. The attacks rely on a the victim opening a malicious PDF file to infect them. Microsoft has issued a recommended workaround for the flaw while it prepares a patch: rerouting the ND proxy service to Null.sys.”]