Experian, the credit checking firm, has bought American online credit monitoring business Mighty Net for $207.5m (£133.2m).The UK company says the US group's consumer marketing brands are highly complementary to Experian's own suite of credit monitoring brands.Mighty, founded 14 years ago, provides bureau reports, bureau scores, credit score tracking and credit file monitoring services.Experian predicts "significant" cost synergies in technology, infrastructure and back office functions which it thinks could save $4m in the year to 31 March 2012 and $5-6m the year after. In 2009, Mighty generated revenue of $115m and earnings before interest and tax (EBIT) of $28m, and is expected t0 grow revenue by 10% in 2010.