{"id":96097,"date":"2019-01-07T16:23:08","date_gmt":"2019-01-08T00:23:08","guid":{"rendered":"https:\/\/cryptoslate.com\/?p=96097"},"modified":"2026-04-25T18:58:40","modified_gmt":"2026-04-25T17:58:40","slug":"ethereum-classic-experiencing-51-percent-attack-immutability-violated","status":"publish","type":"post","link":"https:\/\/cryptoslate.com\/ethereum-classic-experiencing-51-percent-attack-immutability-violated\/","title":{"rendered":"Ethereum Classic Experiencing 51 Percent Attack, Immutability Violated"},"content":{"rendered":"<p>Ethereum Classic experienced a vicious 51 percent attack that allowed attackers\u00a0to conduct eleven deep chain reorganizations and double-spend 88,500 ETC, worth over $400,000. In response to the attack, the price of ETC has plummeted and services using the cryptocurrency have halted.<\/p>\n<p>On Jan. 5th at 13:27 UTC, <a href=\"https:\/\/cryptoslate.com\/coins\/ethereum-classic\/\">Ethereum Classic<\/a> was reorganized at block <a href=\"https:\/\/minergate.com\/blockchain\/etc\/block\/0x086f8a22652bb944475828899e2fc374291cbae96c3925b25eaf36aa8cb4f87a\">7245623<\/a>, and over the course of the next three days the intensity of these attacks increased as the cryptocurrency\u2019s immutability was violated.<\/p>\n<p><a href=\"https:\/\/twitter.com\/etherchain_org\/status\/1082329360948969472\">Bitfly<\/a>, <a href=\"https:\/\/blog.coinbase.com\/ethereum-classic-etc-is-currently-being-51-attacked-33be13ce32de\">Coinbase<\/a>, <a href=\"https:\/\/twitter.com\/Poloniex\/status\/1082374403185430528\">Poloniex<\/a>, and <a href=\"https:\/\/status.kraken.com\/incidents\/n31wl183hqmc\">Kraken<\/a> have all made announcements confirming the attack. Many exchanges and platforms have halted ETC-related services until the attacks subside.<\/p>\n<figure id=\"attachment_94692\" aria-describedby=\"caption-attachment-94692\" style=\"width: 300px\" class=\"wp-caption alignright\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-94692 size-medium\" src=\"https:\/\/cryptoslate.com\/wp-content\/uploads\/2018\/12\/btc-51-attack-social-300x158.jpg\" alt=\"\" width=\"300\" height=\"158\" srcset=\"https:\/\/cryptoslate.com\/wp-content\/uploads\/2018\/12\/btc-51-attack-social-300x158.jpg 300w, https:\/\/cryptoslate.com\/wp-content\/uploads\/2018\/12\/btc-51-attack-social-768x403.jpg 768w, https:\/\/cryptoslate.com\/wp-content\/uploads\/2018\/12\/btc-51-attack-social-1024x538.jpg 1024w, https:\/\/cryptoslate.com\/wp-content\/uploads\/2018\/12\/btc-51-attack-social.jpg 1200w\" sizes=\"(max-width: 300px) 100vw, 300px\" \/><figcaption id=\"caption-attachment-94692\" class=\"wp-caption-text\">Related:\u00a0<a href=\"https:\/\/cryptoslate.com\/explained-51-percent-attacks-on-bitcoin-cryptocurrencies\/\">Deep-Dive Into 51 Percent Attacks<\/a><\/figcaption><\/figure>\n<p>Coinbase <a href=\"https:\/\/blog.coinbase.com\/ethereum-classic-etc-is-currently-being-51-attacked-33be13ce32de\">detected<\/a>\u00a0eleven distinct deep chain reorganizations, nine of which facilitated double-spends. Based on the exchange\u2019s estimates, the attackers were able to double-spend 88,500 ETC, worth over $400,000.<\/p>\n<p>That said, the price of ETC is rapidly dropping in response to the attack, losing 10 percent of its value in the last 24 hours. Over the course of the attack, Ethereum Classic went from $5.50 to $4.90 per coin.<\/p>\n<p>The attacker has been <a href=\"https:\/\/gastracker.io\/miner\/0x3ccc8f7415e09bead930dc2b23617bd39ced2c06\">identified<\/a>. Within the last day, the attack stopped on Jan. 7th, at 05:30 UTC when the attacker\u2019s control of total mining power fell below 50 percent, but the situation may be temporary:<\/p>\n<figure id=\"attachment_96099\" aria-describedby=\"caption-attachment-96099\" style=\"width: 1181px\" class=\"wp-caption alignright\"><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-96099\" src=\"https:\/\/cryptoslate.com\/wp-content\/uploads\/2019\/01\/ethereum-classic-51-percent-attack-mining-pools.png\" alt=\"\" width=\"1181\" height=\"755\" srcset=\"https:\/\/cryptoslate.com\/wp-content\/uploads\/2019\/01\/ethereum-classic-51-percent-attack-mining-pools.png 1181w, https:\/\/cryptoslate.com\/wp-content\/uploads\/2019\/01\/ethereum-classic-51-percent-attack-mining-pools-300x192.png 300w, https:\/\/cryptoslate.com\/wp-content\/uploads\/2019\/01\/ethereum-classic-51-percent-attack-mining-pools-768x491.png 768w, https:\/\/cryptoslate.com\/wp-content\/uploads\/2019\/01\/ethereum-classic-51-percent-attack-mining-pools-1024x655.png 1024w\" sizes=\"(max-width: 1181px) 100vw, 1181px\" \/><figcaption id=\"caption-attachment-96099\" class=\"wp-caption-text\">Chart courtesy <a href=\"https:\/\/gastracker.io\/stats\/miners\">GasTracker.io<\/a><\/figcaption><\/figure>\n<p>If the attacker is able to regain over 50 percent of the network\u2019s mining power, then the attacks may once again continue.<\/p>\n<h2>51 Percent Attacks and Reorganizations Explained<\/h2>\n<p>An attack can occur when one miner is able to amass 50 percent of the hashing power, allowing that miner to \u2018outvote\u2019 honest miners. This means that the attacker could statistically maintain the longest chain and determine which transactions to include on the blockchain.<\/p>\n<p>This invalidates one of the issues the blockchain solves under normal conditions\u2014double spending\u2014where a user spends the same cryptocurrency multiple times.<\/p>\n<p>It is likely that the attacker mined privately for some time before revealing the longer chains. In this case, everything on the Ethereum Classic blockchain would look normal. Then, the miner suddenly goes online and publishes a long string of valid blocks and invalidates a large number of transactions (called a &#8216;reorganization' or &#8216;reorg.'), replacing the old segment of the chain with the attacker\u2019s new segment.<\/p>\n<figure id=\"attachment_94704\" aria-describedby=\"caption-attachment-94704\" style=\"width: 662px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-94704 size-full\" src=\"https:\/\/cryptoslate.com\/wp-content\/uploads\/2018\/12\/2018-12-09-22_58_11-Replacement-attack.xml_.png\" alt=\"\" width=\"662\" height=\"251\" srcset=\"https:\/\/cryptoslate.com\/wp-content\/uploads\/2018\/12\/2018-12-09-22_58_11-Replacement-attack.xml_.png 662w, https:\/\/cryptoslate.com\/wp-content\/uploads\/2018\/12\/2018-12-09-22_58_11-Replacement-attack.xml_-300x114.png 300w\" sizes=\"(max-width: 662px) 100vw, 662px\" \/><figcaption id=\"caption-attachment-94704\" class=\"wp-caption-text\">Original diagram by CryptoSlate<\/figcaption><\/figure>\n<p>By conducting transactions on the honest chain prior to the attack, and once the attacker\u2019s conflicting transactions on the attacking chain are revealed, the honest transactions are subsequently nullified.<\/p>\n<p>These large scale attacks are typically performed against cryptocurrency exchanges. By depositing coins into an exchange the attacker can trade at-risk Ethereum Classic for Bitcoin or another valuable cryptocurrency. Then, the attacker can revert these transactions to regain the Ethereum Classic.<\/p>\n<p>The attacker can continue to plunder in this fashion so long as they maintain control over 50 percent of the network\u2019s mining capability. To learn more about 51 percent attacks read CryptoSlate\u2019s <a href=\"https:\/\/cryptoslate.com\/explained-51-percent-attacks-on-bitcoin-cryptocurrencies\/\">deep-dive<\/a>.<\/p>\n<p>The reorganizations emphasize the vulnerability of smaller proof-of-work cryptocurrencies. It is unknown how long Ethereum Classic will endure this attack, but, for the time being, it is recommended that holders halt any transactions with the cryptocurrency to prevent their transactions from being reverted.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Ethereum Classic experienced a vicious 51 percent attack that allowed attackers\u00a0to conduct eleven deep chain reorganizations and double-spend 88,500 ETC, worth over $400,000. In response to the attack, the price of ETC has plummeted and services using the cryptocurrency have halted. On Jan. 5th at 13:27 UTC, Ethereum Classic was reorganized at block 7245623, and [&hellip;]<\/p>\n","protected":false},"author":29,"featured_media":96100,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[16041,15323],"tags":[],"post_folder":[],"acf":[],"yoast_head":"<!-- This site is optimized with the Yoast SEO Premium plugin v21.9 (Yoast SEO v21.9.1) - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>Ethereum Classic Experiencing 51 Percent Attack, Immutability Violated<\/title>\n<meta name=\"description\" content=\"Ethereum Classic experienced a vicious 51 percent attack that allowed attackers\u00a0to conduct eleven deep chain reorganizations and double-spend 88,500 ETC, worth over $400,000.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/cryptoslate.com\/ethereum-classic-experiencing-51-percent-attack-immutability-violated\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Ethereum Classic Experiencing 51 Percent Attacked, Immutability Violated\" \/>\n<meta property=\"og:description\" content=\"Ethereum Classic experienced a vicious 51 percent attack that allowed attackers\u00a0to conduct eleven deep chain reorganizations and double-spend 88,500 ETC, worth over $400,000.\" \/>\n<meta property=\"og:url\" content=\"https:\/\/cryptoslate.com\/ethereum-classic-experiencing-51-percent-attack-immutability-violated\/\" \/>\n<meta property=\"og:site_name\" content=\"CryptoSlate\" \/>\n<meta property=\"article:published_time\" content=\"2019-01-08T00:23:08+00:00\" \/>\n<meta property=\"article:modified_time\" content=\"2026-04-25T17:58:40+00:00\" \/>\n<meta property=\"og:image\" content=\"https:\/\/cryptoslate.com\/wp-content\/uploads\/2019\/01\/eth-classic-attack-social.jpg\" \/>\n\t<meta property=\"og:image:width\" content=\"1200\" \/>\n\t<meta property=\"og:image:height\" content=\"630\" \/>\n\t<meta property=\"og:image:type\" content=\"image\/jpeg\" \/>\n<meta name=\"author\" content=\"Mitchell Moos\" \/>\n<meta name=\"twitter:card\" content=\"summary_large_image\" \/>\n<meta name=\"twitter:title\" content=\"Ethereum Classic Experiencing 51 Percent Attack, Immutability Violated\" \/>\n<meta name=\"twitter:creator\" content=\"@cryptoslate\" \/>\n<meta name=\"twitter:site\" content=\"@cryptoslate\" \/>\n<meta name=\"twitter:label1\" content=\"Written by\" \/>\n\t<meta name=\"twitter:data1\" content=\"Mitchell Moos\" \/>\n\t<meta name=\"twitter:label2\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data2\" content=\"4 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\/\/schema.org\",\"@graph\":[{\"@type\":\"NewsArticle\",\"@id\":\"https:\/\/cryptoslate.com\/ethereum-classic-experiencing-51-percent-attack-immutability-violated\/#article\",\"isPartOf\":{\"@id\":\"https:\/\/cryptoslate.com\/ethereum-classic-experiencing-51-percent-attack-immutability-violated\/\"},\"author\":{\"@type\":\"Person\",\"@id\":\"https:\/\/cryptoslate.com\/author\/mitchell-moos\/#person\",\"name\":\"Mitchell Moos\",\"url\":\"https:\/\/cryptoslate.com\/author\/mitchell-moos\/\",\"mainEntityOfPage\":{\"@id\":\"https:\/\/cryptoslate.com\/author\/mitchell-moos\/\"},\"image\":{\"@type\":\"ImageObject\",\"@id\":\"https:\/\/cryptoslate.com\/author\/mitchell-moos\/#authorimage\",\"url\":\"https:\/\/cryptoslate.com\/wp-content\/uploads\/2018\/11\/author-mitchell-moos.jpg\",\"contentUrl\":\"https:\/\/cryptoslate.com\/wp-content\/uploads\/2018\/11\/author-mitchell-moos.jpg\",\"caption\":\"Mitchell Moos\"},\"jobTitle\":\"Contributing Analyst\",\"description\":\"Mitchell is a software enthusiast and entrepreneur. 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