A total of 94% of the U.S. merger and acquisition deals announced in 2013 that were valued at more than $100 million were challenged in shareholder lawsuits, according to a new survey.

This continues a trend that began in 2010 of shareholders challenging at least 90% of M&A deals, said the survey by Boston-based Cornerstone Research Inc. There were 612 M&A lawsuits filed last year, according to the survey released Thursday, March 14.

According to the report, M&A lawsuits usually take the form of a class action, with plaintiff attorneys typically alleging the target's board of directors violated its fiduciary duties by conducting a flawed sales process that failed to maximize shareholder value.

Common charges include the failure to conduct a sufficiently competitive sale; the existence of restrictive deal protections that discouraged additional bids; conflicts of interest, such as executive retention; and the target board's failure to disclose enough information about the sale and the financial adviser's valuation.

• As in prior years, multiple lawsuits were filed for most deals, with an average of five lawsuits for deals valued at more than $100 million, and 6.2 average lawsuits filed for deals valued at more than $1 billion.

• The “race to file” has apparently subsided, with the first lawsuit filed an average of 11.7 days after the deal announcement in 2013, compared with 9.3 days in 2012 and 6.5 days in 2009.

• A total of 62% of the deals were litigated in more than one court, with the biggest percentage, 54%, filed in two courts. A total of 38% were filed in just one court, and 8% were filed in three or more courts, a percentage that has declined by half over the last two years, said the survey.

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• The most active courts for M&A litigation, after the Delaware Court of Chancery, were Manhattan at 39, Santa Clara County, Calif., at 30 and Harris County, Texas, at 27.

• The trend of most litigation being resolved before the deal closed continued, with 75% of 2013 deals being resolved at by that point. Of these, 88% were settled, 9% withdrawn by plaintiffs and 3% dismissed by courts, said the survey. Lawsuits that were not settled before the final closing remained pending for as long as four years, according to the study.

Observers have noted that merger objection cases are generally http://www.businessinsurance.com/article/20130127/NEWS07/301279990 settled relatively quickly because of pressure to complete these deals.

Copies of the study, “Shareholder Litigation Involving Mergers and Acquisitions,” are available here.