BERLIN — Weighing in at a hefty 11 pounds, with a tiny 128 MB of working memory and a decades-old Pentium III processor, a used laptop recently bought by a German cybersecurity firm had its heyday long before the first iPhone was built.

But the laptop’s new owner says it has one standout feature: Its hard drive carried — without encryption or even password protection — a confidential user manual and schematics for a surface-to-air missile system that Germany’s air force still uses.

“How the computer ended up on eBay is currently unclear,” Nadine Krüger, a spokeswoman for Germany’s defense ministry, said on Tuesday. The ministry is investigating how the laptop was sold with its hard drive intact and easily accessible.

The systems it contained could not be used to control missiles, let alone launch them, according to defense ministry information. But its embarrassing sale on eBay underscores the major personnel and equipment problems that have plagued the German federal armed forces, which are considered a key component of NATO, since even before President Trump’s repeated calls for Germany to increase its military spending.