How to maintain history of products viewed by user in ASP.Net

hi

I have product.aspx page  that users can see all product on this page and if they click on product they go to viewproduct.aspx 

Now I want when users saw some product detail's(i.e they see 4 product details-->go to viewproduct.aspx) when they come back to product.aspx page in product.aspx page is datalist that in this datalist show viewed product by users...

i.e here if user see 4 product details, in product.aspx in datalist show 4 image of viewed product...

can you help me in this issue?

best regards

neda