HP-Autonomy ($11 Billion, 2011)

HP's 2011 acquisition of Autonomy for $11 billion, an 80% premium, stands as the most notorious write-off in tech M&A history. Within a year, HP wrote down $8.8 billion, alleging Autonomy inflated revenue through accounting irregularities, leading to criminal fraud charges. This loss is three times larger than the average failed acquisition in the sector, vastly outperforming #6 Daimler-Chrysler in shareholder destruction.