Vodafone sacked or disciplined 429 employees for fraud or ethical breaches last year, according to figures revealed in its annual corporate responsibility report.
The mobile communications giant also dismissed or warned 186 contractors during 2007-08.
Of these 615 cases, seven related to incidents of fraud exceeding €20,000 (£15,850). The remaining 608 disciplinary cases related to incidents below that value.
A significant number of the incidents (216 cases) related to theft of money or handsets, SIM cards and other equipment. Other incidents involved manipulation of customer accounts (182 cases) and the unauthorised release of customer information (67 cases).
Vodafone said the increase in reported cases of internal fraud was due to improved reporting methodology across the organisation. Each operating company now reports monthly by business area and by type of fraud or crime.
The company said it was using the information gathered to roll out an internal fraud and crime reduction and awareness programme to all operating companies.
Vodafone employs 71,000 people globally, 11,700 of which are based in the UK.