The Brain Tumour Foundation of Canada says it was horrified to learn fraudsters were collecting cheques on its behalf then altering them to show higher amounts.  Spokeswoman Amy Mathias says the foundation learned about the con from one of its donors who had a cheque altered.   Mathias says the foundation does not raise money with door-to-door solicitations.  Rather it uses a national walk event.    In North Bay, the foundation holds its annual walk June 4th and the day before, the walk goes in Sudbury where fraudsters started their con last January.   Mathias is hopeful that the scammers haven’t damaged the reputation of the foundation.   In Sudbury, when police learned about the con, they advised people who thought they were donating to the foundation to check their records to ensure their cheques weren’t altered.