Not even the National Security Agency is immune to carelessness, according to noted leaker Edward Snowden. The agency\u2019s operatives can get lazy, and sometimes they leave behind files inside the servers they\u2019ve hacked.That could explain how an anonymous group managed to obtain hacking tools that may belong to the NSA. The files are up for auction to the highest bidder, and allegedly include cyber weapons that rival the Stuxnet computer worm.CounterhackingOn Tuesday, Snowden, a former NSA contractor, tweeted that it isn\u2019t \u201cunprecedented\u201d for cyberspies to try to hack the agency\u2019s malware staging servers.The NSA itself routinely hacks into servers used by opposing groups, Snowden added. This is how the agency can steal rival hacking tools, and it can lurk undetected on these servers for years.But the \u201cNSA is not made out of magic,\u201d Snowden said. \u201cOur rivals do the same thing to us -- and occasionally succeed." NSA operatives are told to never leave behind any hacking tools they use on servers, \u201cbut people get lazy,\u201d Snowden said. \u00a0It\u2019s still unclear if the tools actually belong to the NSA. The anonymous hackers who obtained them claim they were stolen from the Equation Group, a top cyberespionage team that may be linked to the NSA and may have helped develop the Stuxnet worm. \u00a0The hackers have posted sample files online, and the files contain numerous exploits, implants, and tools for firewall and router products from Cisco, Juniper Networks, Fortinet, and Chinese vendor Topsec, according to security researchers. \u00a0(A list of the exploits can be found here.)Free exploitsBrian Martin, a director of vulnerability intelligence at Risk Based Security, said he was surprised the hackers offered up these exploits as free samples.\u201cThese exploits have a huge value,\u201d and normally hackers would never give them away, he said.For instance, a few of the exploits target Cisco products -- which are widely used and thought to be secure and stable -- \u00a0and can allow a bad actor to bypass a firewall, Martin said.Risk Based Security is still looking at how severe these exploits might be, and if they've previously been patched. But the stolen hacking tools might be old, the company noted.The sample files that have been released were dated most recently to 2013. This suggests that the NSA probably wasn\u2019t hacked directly, Martin said.The NSA hasn\u2019t commented on the alleged leak. Cisco, however, said Tuesday it was investigating the exploits. \u201cSo far, we have not found any new vulnerabilities related to this incident,\u201d the company said.A political message?However, a potentially more alarming issue is what else might have been stolen.The hackers, who call themselves the Shadow Brokers, have warned they\u2019ve obtained other cyber weapons that could wreck havoc on financial systems.\u201cWe auction best files to highest bidder. Auction files better than Stuxnet,\u201d the hackers said in posts on Github and Tumblr that were later taken down.Security experts suspect that the Shadow Brokers may actually be foreign spies who are trying to threaten the U.S.\u201cWhoever stole this data now wants the world to know,\u201d Nicholas Weaver, a security researcher at the\u00a0International Computer Science Institute in California, wrote in a blog post.He and other security researchers have noted the timing of the auction. It comes as the U.S. is investigating whether Russian state-sponsored hackers may have stolen sensitive files from the Democratic National Committee.The Shadow Brokers, however, have painted themselves as hacktivists who oppose \u201cwealthy elites.\u201d Their auction is still up for bids and accepting bitcoin.Although the Shadow Brokers are offering no guarantees with their auction, the sale probably isn\u2019t a scam. On Tuesday, security firm Kaspersky Lab found further evidence that Shadow Brokers did indeed steal files from the Equation Group.