The Kerala Police has issued an advisory for public asking people to be cautious of spam numbers. The cops issued a public circular in the state asking the public not to attend\/call back on phone numbers starting with +4 and +5 as they look to be suspicious and unknown. The announcement was issued after several people reported that they received such call from numbers starting with +4 and +5. The numbers are believed to be from countries like Bolivia. The international code for Bolivia is +591. The Kerala police said that its high-tech wing has begun a probe in synchronicity with the complainants. The police is trying to find the source of the call and the intent of it. It is not clear whether these calls are coming from outside the country or whether they are being made to appear as ISD calls, according to Indian Express report. People told Indian Express that they experienced a significant reduction in their smartphone 'talk-time' when they called back on the number starting with +4 and +5 after receiving a missed call. In such cases, the police have advised people not to receive or call back on those suspicious phone numbers.